Water surface evaporation capacity monitoring method with rainfall compensation

Abstract

The invention discloses a water surface evaporation capacity monitoring method with rainfall compensation, and the method comprises the steps: obtaining the water level balance lag time between an evaporation dish and a liquid level logging well according to a connection structure of the liquid level logging well and the evaporation dish; the water level in the liquid level logging well is collected regularly; a rain gauge is adopted to regularly monitor whether rainfall occurs or not and the corresponding rainfall capacity; correcting the current evaporation capacity calculation period by adopting the water level balance lag time to obtain a corrected evaporation capacity calculation period, and fitting to obtain a change curve of the water level of the corrected evaporation capacity calculation period along with time; the rainfall type is judged by combining a rainfall signal fed back by the rain gauge or a change curve of the water level along with time; according to different rainfall types, the rainfall capacity is estimated by combining the water level data in the liquid level logging well and the measurement data of the rain gauge, the estimated rainfall capacity is adopted to compensate the water level difference value of the evaporation capacity calculation period, and the evaporation capacity is obtained through calculation. The measuring precision of the water surface evaporation capacity can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of evaporation monitoring, and in particular to a water surface evaporation monitoring method with rainfall compensation. Background Art

[0002] Water surface evaporation refers to the amount of water that is dispersed into the air through evaporation from the water surface during a certain period of time, usually expressed in millimeters of the thickness of the evaporated water layer. The measurement of water surface evaporation can be observed through an evaporator. Water surface evaporation is very important in hydrological and meteorological research. For example, in arid areas, if the evaporation is much greater than the precipitation, it will lead to severe drought. In addition, sea surface evaporation also has an important impact on marine climate and marine ecology.

[0003] The calculation methods of water surface evaporation can be roughly divided into two categories: one is the theoretical calculation method, and the other is the empirical calculation method. The so-called theoretical calculation method is a method with a strong physical basis, such as the heat balance method, the aerodynamic method and the water balance method. These calculation methods use the principles and theories of heat balance, aerodynamics and water balance to determine the evaporation of the water surface. Theoretical calculation methods mainly include the heat balance method, the aerodynamic method, the comprehensive method and the water balance method. The empirical calculation method is generally a method of estimating the evaporation of the water surface based on the measured data and using empirical formulas when the accuracy requirements for the measured data are not very high. In addition, there is another more common method, namely the instrument measurement method.

[0004] The instrument measurement method uses an evaporation dish. The whole set of equipment includes the control part, the liquid level logging part, the water replenishment overflow part, the water replenishment tower and other main parts. By measuring the water level changes in the liquid level logging well, the evaporation of water surfaces of different areas can be calculated. However, ordinary evaporation dishes can only be used for the natural evaporation of water when there is no rainfall. Once rainfall occurs, the liquid level logging well will have additional rainwater, which will cause errors in the evaporation calculation results. To this end, the researchers added a special rain gauge to the existing evaporation dish to measure the rainfall and correct the evaporation according to the rainfall counted by the rain gauge. However, this method still has the following problems: First, based on the tipping bucket measurement principle of the rain gauge, for some rainfall situations, for example, when the rainfall is small, the rainwater accumulates slowly in the rain gauge, and the rainfall signal will not be generated until a long time later. For rainfall statistics, this part of the rainfall value can be ignored, but for evaporation statistics, this part of the rainfall value will cause a large error. Second, when it rains, raindrops frequently fall into the liquid level logging well, affecting the stability of the water surface in the liquid level logging well. At the same time, the water level changes in the liquid level logging well caused by the additional rainwater cannot be transmitted to the water level meter in the first time, causing errors in the final water level statistical results.

[0005] In addition, most of the conventional evaporation models currently use data from simple rain sensors (tipping bucket or weighing type) to replace rainfall in evaporation calculations. However, due to certain errors in the rain gauge, including errors caused by the inconsistency between the rain gauge and the evaporation dish's rain-receiving diameter and the measurement error of the rain gauge itself, errors may also occur in evaporation calculations.

[0006] Therefore, due to the limitations of the liquid level logging structure and measuring device, once it rains, uncontrollable errors will occur in evaporation. For the evaporation amount, which is already small in value, these errors are enough to significantly reduce the monitoring accuracy. Summary of the invention

[0007] The present invention classifies and studies the characteristics of liquid level logging during rainfall, and proposes a water surface evaporation monitoring method with rainfall compensation, which effectively improves the measurement accuracy of water surface evaporation.

[0008] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0009] The present invention discloses a water surface evaporation monitoring method with rainfall compensation, the water surface evaporation monitoring method comprising the following steps:

[0010] S1, design a water level balance test according to the connection structure of the liquid level logging well and the evaporation dish to obtain the water level balance lag time between the evaporation dish and the liquid level logging well;

[0011] S2, regularly collect the water level in the liquid level logging well, and store the collected water level value and the corresponding collection time in the water level database; use a rain gauge to regularly monitor whether rainfall occurs and the corresponding rainfall amount;

[0012] S3, in a new evaporation calculation cycle, using the water level balance lag time to correct the current evaporation calculation cycle to obtain a corrected evaporation calculation cycle, and fitting to obtain a curve of the change of the water level over time in the corrected evaporation calculation cycle;

[0013] S4, judging the rainfall type in combination with the rainfall signal fed back by the rain gauge or the water level variation curve over time, the rainfall types include no rainfall, light rainfall, moderate rainfall and heavy rainfall; wherein, light rainfall means that no rainfall signal fed back by the rain gauge is received, but the water level variation curve over time during the evaporation calculation period reflects rainfall; moderate rainfall means that the rainfall signal fed back by the rain gauge is received and the maximum water level value does not exceed the overflow line water level; heavy rainfall means that the maximum water level value after rainfall exceeds the overflow line water level and the rainfall period is within the evaporation calculation period;

[0014] S5, in the case of no rainfall, the evaporation amount of the current evaporation amount calculation period is calculated by combining the water level change value of the evaporation amount calculation period calculated by combining the water level balance lag time;

[0015] In the case of slight rainfall, the evaporation of the current evaporation calculation period is predicted by combining the evaporation type of the study area, the evaporation change curve of the previous N evaporation calculation periods, and the water level change curve of the revised evaporation calculation period over time;

[0016] In the case of moderate rainfall, the rainfall start time is corrected in combination with the water level balance lag time to calculate the rainfall in the current evaporation calculation period; the water level change value in the evaporation calculation period is corrected using the calculated rainfall to calculate the evaporation in the current evaporation calculation period;

[0017] In the case of heavy rainfall, the overflow period is selected according to the water level. For each overflow period, the rainfall output by the rain gauge is used as the rainfall in the overflow period. The rainfall start time is corrected in combination with the water level balance lag time, and the rainfall in the non-overflow period is calculated in combination with the water level value. The total rainfall is used to correct the water level change value of the evaporation calculation period, and the evaporation of the current evaporation calculation period is calculated.

[0018] Furthermore, when receiving the rainfall change signal fed back by the rain gauge, the first rainfall change signal is taken as the rainfall start signal, and the last rainfall change signal is taken as the rainfall end signal; the last rainfall change signal means that there is no new rainfall change signal within a preset time range after the rainfall change signal; the time between the rainfall start signal and the corresponding rainfall end signal is taken as a rainfall period.

[0019] Furthermore, in combination with the rainfall signal fed back by the rain gauge or the water level change curve over time, the process of determining the rainfall type includes the following steps:

[0020] A1, determine whether the rainfall change signal fed back by the rain gauge is received during the evaporation calculation period, if yes, it is determined that there is rainfall, then further determine whether the rainfall type is medium rainfall or heavy rainfall according to whether the real-time water level reaches the overflow water level, and end the process, otherwise, go to step A2;

[0021] A2, divide the evaporation calculation period into several statistical periods, and draw the historical evaporation-time curve based on the historical evaporation data when there is no rainfall, taking a single statistical period as the basic time unit;

[0022] A3, analyze the historical evaporation-time curve to obtain the evaporation proportion law of different statistical periods within an evaporation calculation cycle or the evaporation range of each statistical period when there is no rainfall;

[0023] A4, fitting to obtain the water level variation curve over time of the modified evaporation calculation period, calculating and drawing the evaporation-time curve of the current evaporation calculation period, judging whether each statistical period conforms to the evaporation proportion law or the corresponding evaporation interval, if all conform, judging that there is no rainfall, and ending the process, otherwise, marking the non-conforming statistical period as an abnormal period, and proceeding to step A5;

[0024] A5, with 5 minutes as an analysis cycle, draws the water level change curve during the abnormal period; judges whether rainfall occurs in the current analysis cycle based on the water level change slope of the adjacent analysis cycle. If rainfall occurs, it is determined that light rainfall occurs in the current evaporation calculation cycle.

[0025] Furthermore, in step A4, for each analysis period, water level values ​​are collected 10 times with a period of 30 seconds, and the average value of the 10 water level values ​​is taken as the water level value of the current analysis period.

[0026] Furthermore, for the case of no rainfall, the evaporation calculation formula is:

[0027] E=h1-h2

[0028] Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

[0029] Furthermore, for the case of light rainfall, the process of predicting the evaporation in the current evaporation calculation period includes the following steps:

[0030] B1, collect the historical evaporation change curves of different study areas, analyze the evaporation change curves of each study area when there is no rainfall, manually mark the evaporation type according to the evaporation ratio of the time period, and construct the first data set;

[0031] B2, using the first constructed data set to train the convolutional neural network to obtain an evaporation type recognition model;

[0032] B3, import the historical evaporation change curve of the study area into the trained evaporation type recognition model, and output the corresponding evaporation type of the study area;

[0033] B4, according to the evaporation type of the current study area, the evaporation change curve of the study area with the same evaporation type without rainfall is imported into the LSTM network for training to obtain the evaporation prediction model corresponding to the study area;

[0034] B5, the evaporation of the first N evaporation calculation cycles is calculated according to the water level change curve of the first N evaporation calculation cycles, and the evaporation is imported into the trained evaporation prediction model to predict the evaporation of the current evaporation calculation cycle.

[0035] Furthermore, for the case of moderate rainfall, the calculation process of the rainfall in the current evaporation calculation cycle includes the following steps:

[0036] C1, if the rainfall end signal occurs in the current evaporation calculation cycle, the rainfall in the current evaporation calculation cycle is calculated using the following formula:

[0037]

[0038] In the formula, h px1 Indicates the water level value X hours before the rainfall start signal; h p1max Indicates the highest water level value within 1 hour before the rainfall signal; h px2 Indicates the water level value for X periods of time after the rainfall end signal is generated or the next evaporation calculation cycle ends; go to step B4; otherwise, go to step B2;

[0039] C2, determine whether the accumulated duration of the evaporation amount not updated period is greater than the preset duration threshold, if so, proceed to step B3, otherwise, report the evaporation amount of the last stable period, and the evaporation amount not updated period is increased by one;

[0040] C3, calculate the rainfall in the current evaporation calculation period according to the following formula:

[0041] p=h px2 -h p1max ;

[0042] C4, the evaporation is calculated using the following formula:

[0043] E=h1-h2+p

[0044] Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

[0045] Furthermore, in the case of heavy rainfall, the water level in the level logging well is collected in real time with a collection period of 5 minutes;

[0046] For each collection period, the water level in the collected level logging well is compared with the preset overflow water level. If the water level in the level logging well exceeds the overflow water level, the collection period is marked as the overflow period, and the rainfall output by the rain gauge is used as the rainfall in this period;

[0047] For the non-overflow period, the rainfall start time is corrected by combining the water level balance lag time, and the rainfall in the non-overflow period is calculated:

[0048]

[0049] In the formula, hpx3 Indicates the water level value when overflow begins;

[0050] Combining the rainfall p1 during the non-overflow period and the rainfall p2 during the overflow period, the rainfall under heavy rainfall conditions is obtained as P = p1 + p 2， Correct the evaporation to get the evaporation:

[0051] E = h1 - h2 + p;

[0052] Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

[0053] Furthermore, the rainfall type includes continuous rainfall; continuous rainfall means that the maximum water level after rainfall exceeds the overflow line water level, and the rainfall period covers more than one evaporation calculation cycle; the evaporation monitoring process during continuous rainfall includes the following steps:

[0054] D1, determine whether the duration of the evaporation calculation cycle is less than a preset duration threshold, if so, proceed to step D2;

[0055] D2, based on the evaporation change curve of the evaporation calculation period at the beginning of rainfall when there is no rainfall, select the one with the highest similarity from the evaporation change curves of the same period in the past N days, and report the evaporation of the selected evaporation change curve at the same time on the same day as the reference evaporation of each evaporation calculation period during continuous rainfall; end the process;

[0056] D3, for the evaporation calculation cycle at the beginning of rainfall, the rainfall period is divided into multiple overflow periods, and the rainfall output by the rain gauge is used as the rainfall in the overflow period. For the rainfall in the non-overflow period, the formula is used. Calculate the rainfall; obtain the total rainfall in the evaporation calculation period from the beginning of rainfall, and draw the evaporation-time variation curve when there is no rainfall;

[0057] According to the water level value of the evaporation calculation period at the end of rainfall, the evaporation-time variation curve when there is no rainfall in the evaporation calculation period at the end of rainfall is drawn;

[0058] Combining the evaporation change curves over time in the rainless periods of the two evaporation calculation cycles at the beginning and end of rainfall, as well as the rainfall at the beginning of rainfall, a curve of evaporation change over time in the study area in one evaporation calculation cycle was fitted. The evaporation calculated based on this curve was used as the evaporation for all evaporation calculation cycles during continuous rainfall.

[0059] Furthermore, if the rainfall-free periods in the two evaporation calculation cycles at the beginning and end of rainfall cannot cover the entire evaporation calculation cycle, the one with the highest similarity is selected from the evaporation change curves of the past N days based on the drawn part, and it is used as a reference to fit the evaporation-time change curve of the entire evaporation calculation cycle.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] First, the water surface evaporation monitoring method with rainfall compensation of the present invention adopts different rainfall compensation schemes according to different rainfall situations, thereby effectively improving the measurement accuracy of water surface evaporation.

[0062] Second, the water surface evaporation monitoring method with rainfall compensation of the present invention designs a water level balance test according to the connection structure of the liquid level logging well and the evaporation dish, obtains the water level balance lag time between the evaporation dish and the liquid level logging well, and uses the water level balance lag time to correct the water level value, thereby reducing the error caused by the evaporation dish structure.

[0063] Third, the water surface evaporation monitoring method with rainfall compensation of the present invention is applicable to 20m 2 、5m 2 , 1m 2 The method can be used for evaporating dishes, and there is no need to make any improvements to the existing evaporator structure. It has strong universality and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is a flow chart of the water surface evaporation monitoring method with rainfall compensation of the present invention;

[0065] Figure 2 This is an example diagram of evaporation over a 4-hour period in a certain study area;

[0066] Figure 3 This is a schematic diagram of the 1-hour normal water level change results in a certain research area when there is no rainfall;

[0067] Figure 4 This is a schematic diagram of the water level changes in a certain study area during a 1-hour rainfall period. DETAILED DESCRIPTION

[0068] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0069] See also Figure 1 The present invention discloses a water surface evaporation monitoring method with rainfall compensation, the water surface evaporation monitoring method comprising the following steps:

[0070] S1, according to the connection structure of the liquid level logging well and the evaporation dish, a water level balance test is designed to obtain the water level balance lag time between the evaporation dish and the liquid level logging well.

[0071] S2, regularly collect the water level in the liquid level logging well, and store the collected water level value and the corresponding collection time in the water level database; use a rain gauge to regularly monitor whether rainfall occurs and the corresponding rainfall amount.

[0072] S3, in the new evaporation calculation cycle, the water level balance lag time is used to correct the current evaporation calculation cycle to obtain a corrected evaporation calculation cycle, and a curve of the change of the water level over time in the corrected evaporation calculation cycle is obtained by fitting.

[0073] S4, judging the rainfall type in combination with the rainfall signal fed back by the rain gauge or the curve of water level change over time, which includes no rainfall, light rainfall, moderate rainfall, heavy rainfall and continuous rainfall; wherein, light rainfall means that no rainfall signal is received from the rain gauge, but the curve of water level change over time in the evaporation calculation period reflects rainfall; moderate rainfall means that the rainfall signal is received from the rain gauge and the maximum water level value does not exceed the overflow line water level; heavy rainfall means that the maximum water level value after rainfall exceeds the overflow line water level and the rainfall period is within the evaporation calculation period; continuous rainfall means that the maximum water level value after rainfall exceeds the overflow line water level and the rainfall period covers more than one evaporation calculation period.

[0074] S5, in the case of no rainfall, the evaporation amount of the current evaporation amount calculation period is calculated by combining the water level change value of the evaporation amount calculation period calculated by combining the water level balance lag time.

[0075] In the case of light rainfall, the rainfall is estimated by combining the water level change curves of the first N evaporation calculation cycles and the water level change curve over time of the corrected evaporation calculation cycle. The estimated rainfall is used to correct the water level change value of the evaporation calculation cycle to calculate the evaporation of the current evaporation calculation cycle.

[0076] In the case of moderate rainfall, the rainfall start time is corrected in combination with the water level balance lag time to calculate the rainfall for the current evaporation calculation period; the calculated rainfall is used to correct the water level change value for the evaporation calculation period to calculate the evaporation for the current evaporation calculation period.

[0077] In the case of heavy rainfall, the overflow period is selected according to the water level. For each overflow period, the rainfall output by the rain gauge is used as the rainfall in the overflow period. The rainfall start time is corrected in combination with the water level balance lag time, and the rainfall in the non-overflow period is calculated in combination with the water level value. The total rainfall is used to correct the water level change value of the evaporation calculation period, and the evaporation of the current evaporation calculation period is calculated.

[0078] In the case of continuous rainfall, for each evaporation calculation cycle, the water levels of the current evaporation calculation cycle and the previous evaporation calculation cycle are combined to determine whether to correct the rainfall start time and the rainfall type of the current evaporation calculation cycle, and the evaporation of the current evaporation calculation cycle is calculated based on the judgment results.

[0079] (1) Water level balance lag time

[0080] The evaporator of the present invention also includes the main components such as the control part, the liquid level logging part, the special rain gauge, the water replenishment overflow component, the water replenishment tower, etc. The control part mainly controls the evaporation data collection, calculation, communication and other parts. The IP address, port number, marker line, water replenishment overflow time are set by the mobile phone APP through the Bluetooth communication method. The APP operation interface can also realize manual water replenishment, overflow control, real-time water level collection, etc. The liquid level logging component includes a high-precision magnetostrictive water level gauge, a float, a magnetic ring, etc., with a resolution of 0.024mm, which can realize the measurement of the water level of 0.1mm. The special rain gauge adopts a double-tipping bucket rain gauge to ensure timely collection of rainfall. The water replenishment overflow component includes two self-priming pumps. The water replenishment pump connects the evaporating dish with the water replenishment tower. If there are devices and pools similar to the water replenishment tower on site, the water replenishment tower can be cancelled, and the volume should be greater than 0.8m 3 , the water supply tower should be connected to tap water through a float valve for water supply. The overflow pump connects the evaporation dish and the overflow tank, and discharges the evaporation dish water into the overflow tank. The overflow tank should be dug with a foundation pit and bricked around it, and the water should be drained by natural infiltration. The whole set of equipment needs to be connected to 220V AC, and the RTU power supply and control power are both 12V. The pump is controlled by a relay. The water supply pump and the overflow pump are connected to the evaporation dish through a common pipeline. The other end of the water supply pump is connected to the water supply tank. Both ends of the water supply pipe are equipped with a one-way valve to avoid pressureless backflow. The overflow pump outlet is connected to the filter tank. After sedimentation, the upper clarified part can be used to replenish the water in the water supply tank.

[0081] Since the evaporation dish and the liquid level logging well are connected by a pipe, the water level in the evaporation dish changes when it rains, but the water level between the evaporation dish and the liquid level logging well will reach equilibrium after a period of time. That is, when it rains, the water level in the evaporation dish rises, but it takes a period of time for the water level in the liquid level logging well to rise to the equilibrium position.

[0082] In order to verify the relationship between the size and length of the connecting pipe and the balance time, the present invention designs a water level balance test to obtain the water level balance lag time between the evaporation dish and the liquid level logging. The reference variables include three parameter variables: pipe diameter (4 points, 6 points), pipeline length (1.5m, 4.2m), and the number of bends.

[0083] First, prepare two transparent tanks with a diameter of Φ200. Manual stop valves are installed on both sides of the tanks. One end of the stop valve connects the two tanks. The two sides are connected to tap water (for tank water replenishment) and a pool (for tank water drainage). Different hot-melt pipes and elbows are used for testing according to the test requirements. The test is completed by first closing the connecting pipes in the two tanks, artificially changing the liquid level difference between the two tanks by replenishing water, draining water, etc., and collecting the water level difference and time required before and after the two tanks are balanced through RTU.

[0084] The experimental conclusions are as follows: (1) The length of the pipeline between tanks is proportional to the balance time; (2) The number of pipeline joints between tanks is proportional to the balance time; (3) The diameter of the pipe between tanks is inversely proportional to the balance time; (4) There is a certain coefficient relationship between the tank balance time and the above parameters. At present, a 1.5m long 4-point pipeline design is used between the evaporation dish and the liquid level logging. When there are 4 elbows in the middle, it is tested that the water level balance time (lag) does not exceed 10 minutes. The present invention takes 15 minutes as the water level balance lag time.

[0085] In addition to being obtained from the water level balance test, the water level balance lag time can also be obtained from the analysis of the pipeline parameters between the evaporation dish and the liquid level logging. For the latter, the water level balance lag time between the two is calculated using the following formula:

[0086]

[0087] In the formula, T represents the water level balance lag time; h represents the water level difference between the evaporation dish and the level logging well; s represents the cross-sectional area of ​​the pipeline; λ represents the conversion coefficient, which is related to the number of pipeline joints and pipe material on site; l represents the pipeline length; t represents the basic balance time, which is defined as the balance time required for the lower limit of 5mm liquid level difference and 1.5m pipeline length during on-site measurement. The above formula is based on the design and calculation of the standard pipeline joint measured on site, and can be corrected by using the on-site artificial simulation balance time.

[0088] In the new evaporation calculation cycle, the water level balance lag time is used to correct the current evaporation calculation cycle to obtain the corrected evaporation calculation cycle, and the water level change curve of the corrected evaporation calculation cycle with time is fitted. Assuming that the current evaporation calculation cycle is one day, the corrected evaporation calculation cycle will shift the start time and the end time back by 15 minutes. For example, the measured water level at 0:15 on the same day is selected as the starting water level of the current evaporation calculation cycle, and the measured water level at 0:15 the next day is selected as the ending water level of the current evaporation calculation cycle. The difference between the ending water level and the starting water level is used as the evaporation of the day. In this way, the evaporation error caused by the water level balance lag time can be eliminated, especially when the water level changes suddenly due to some external factors. For example, we set the start time of the new evaporation calculation cycle after water replenishment, and use the water level of the liquid level logging 15 minutes after water replenishment as the starting water level of the current evaporation calculation cycle, which can effectively eliminate the influence of the water level rise caused by water replenishment on the evaporation calculation.

[0089] In addition, the water level balance lag time can also correct the water level rise caused by rainfall during rainfall, avoiding large errors in rainfall calculation results due to sudden changes in water levels caused by rainfall.

[0090] (II) Calculation of rainfall during evaporation

[0091] The present invention introduces a new rainfall method, that is, calculating rainfall by water level. The reasons are: 1. The water level measurement and the evaporation dish are in the same water body, and there is no systematic error; 2. The measurement accuracy of the water level is much greater than the measurement accuracy of the rain gauge. Specifically, the rainfall start time and end time are determined by determining the rainfall sensor signal, and the rainfall time period is obtained, and then the rainfall is calculated by the water level corresponding to the same period. However, this method is only suitable for short-term rainfall or when the rainfall does not overflow. Once a more complex rainfall situation occurs, other adjustments to the rainfall calculation process are required. Based on the above-mentioned calculation of rainfall by water level, the present invention proposes the following rainfall calculation methods for the following rainfall situations.

[0092] (1) Analysis of rainfall types

[0093] The present invention reclassifies rainfall types in view of the rainfall influence in the evaporation calculation process. It should be pointed out that the rainfall types of the present invention are specially classified for evaporation calculation and are not the same as the rainfall types in the conventional sense.

[0094] Rainfall types include no rainfall, light rainfall, moderate rainfall, heavy rainfall and continuous rainfall. Among them, light rainfall means that there is no rainfall signal fed back by the rain gauge, but the water level change curve over time during the evaporation calculation period reflects rainfall; moderate rainfall means that the rainfall signal fed back by the rain gauge is received and the maximum water level does not exceed the overflow line water level; heavy rainfall means that the maximum water level after rainfall exceeds the overflow line water level and the rainfall period is within the evaporation calculation period.

[0095] In the case of light rainfall, it is necessary to determine the rainfall type based on the rainfall signal fed back by the rain gauge or the water level change curve over time.

[0096] According to natural laws, the evaporation of a 4-hour period at the same station within a certain period of time will show a certain regularity, and rainfall will cause the evaporation of the period to be smaller or return to zero. Therefore, this law can be used to set the evaporation standard curve, and then the evaporation curve of the current evaporation calculation period can be compared with the evaporation standard curve to determine whether there is light rainfall.

[0097] See also Figure 2 , Figure 2 This is the daily evaporation curve of a certain study area on January 8, January 9, January 10, and January 11. Figure 2 It can be seen that the maximum 4h evaporation will have a high proportion of peak evaporation according to the law. For this study area, evaporation is concentrated in 8-12 o'clock and 20-0 o'clock, accounting for about 50% of the total evaporation. In the long run, there are upper and lower limits for evaporation in different periods. From this, the law of evaporation proportion in the study area when there is no rainfall and the rainfall range in different periods are summarized. This is because the evaporation in the same study area is still determined by local environmental parameters and geographical parameters, so there will naturally be regularity.

[0098] In practical applications, when the evaporation calculation cycle is one day and the evaporation is relatively stable, the daily average evaporation over a week or longer period can be selected to obtain the daily average evaporation value, and then the average value ±0.4mm (this value is inferred based on the historical evaporation characteristics of the site) is used as the possible variation range. If it is lower or higher than this range, it needs to be marked as doubtful in the results report, and the water level change characteristics should be further analyzed to determine whether light rainfall has occurred.

[0099] For each abnormal period, take 5 minutes as an analysis cycle, draw the water level change curve within the abnormal period, judge whether there is light rainfall in the current analysis period according to the water level change slope of the adjacent analysis period, and get the rainfall period included in the abnormal period. This is because the water level will gradually decrease with natural evaporation, and rainfall (even light rainfall) will cause the water level to increase. Therefore, when the water level rises or falls sharply, such as normal water replenishment, overflow, artificial water change, rainfall and other operations in the system itself, it is an abnormal situation and needs to be judged according to the water level change curve. Figure 3 It is the normal evaporation water level change (1h normal water level change). It can be analyzed that for the study area, the specific constraint is that the water level change every 5 minutes does not exceed ±0.1mm (in order to reduce the water level measurement error, the water level can be sampled 10 times within 30S each time, and the average value of 10 times is used as the basis for water level judgment). When there is light rainfall, the 5-minute water level will be abnormal, such as Figure 4 As shown. Therefore, for the study area, if the 5-minute average water level shows a continuous rise of more than 0.1 mm, or the 5-minute water level does not change for multiple times within 1 hour, it means that micro-rainfall has occurred, and the specific rainfall period when the micro-rainfall occurred can be located at the same time. For different study areas, the 5-minute water level change value is different, but in the absence of rainfall, it will show a continuous slow decline. If the water level is abnormal and cannot be reflected by the 5-minute water level curve, it can be ignored because the value is too small, and it is a change within the allowable range of evaporation monitoring error.

[0100] When receiving the rainfall change signal fed back by the rain gauge, the first rainfall change signal is taken as the rainfall start signal, and the last rainfall change signal is taken as the rainfall end signal; the last rainfall change signal means that there is no new rainfall change signal within the preset time range after the rainfall change signal; the time between the rainfall start signal and the corresponding rainfall end signal is taken as a rainfall period. Then, according to the time when the rainfall end signal occurs and the real-time water level in the liquid level logging well, it is judged whether overflow or cross-cycle occurs, and further judged whether the rainfall type is medium rainfall, heavy rainfall or continuous rainfall.

[0101] (2) When there is no rainfall

[0102] For the case of no rainfall, the evaporation calculation formula is:

[0103] E=h1-h2

[0104] In the formula, h1 represents the average water level collected at the start time of the evaporation calculation cycle; h2 represents the average water level collected at the end time of the evaporation calculation cycle. The evaporation calculation cycle here is the start time and end time corrected by the water level balance lag time.

[0105] (3) Light rainfall

[0106] In the case of slight rainfall, firstly, the historical evaporation change curve of the corresponding study area is analyzed to obtain the evaporation type of the study area and the set of evaporation change curves when there is no rainfall. This step can be completed with the help of convolutional neural network. Specifically, the evaporation change curves of different study areas when there is no rainfall are analyzed, and the evaporation type is manually marked (which can be set according to the evaporation ratio of the time period) to construct a first data set; the convolutional neural network is trained using the constructed first data set, and then the historical evaporation change curve of the current study area is imported into the trained convolutional neural network to output the corresponding evaporation type.

[0107] According to the evaporation type of the current study area, the evaporation change curve of the study area with the same evaporation type without rainfall is imported into the LSTM network for training. Then, the evaporation of the first N evaporation calculation cycles is calculated according to the water level change curve of the first N evaporation calculation cycles, and then imported into the trained LSTM network to predict the evaporation of the current evaporation calculation cycle.

[0108] Preferably, the rainfall can also be estimated based on the water level variation curve over time in the corrected evaporation calculation period and the predicted evaporation in the current evaporation calculation period.

[0109] (4) Moderate rainfall

[0110] In the case of moderate rainfall, the rainfall is generally not very large, overflow will not occur, and the rain gauge will have rainfall start signal and rainfall end signal. However, since the rain gauge itself has a large error, the present invention uses the water level difference to estimate the rainfall. Specifically, the rainfall in an evaporation calculation cycle under moderate rainfall conditions can be calculated using the following formula:

[0111]

[0112] In the formula, h px1 Indicates the water level value 15 minutes before the rainfall start signal; h p1max Indicates the highest water level value within 1 hour before the rainfall signal; h px2 Indicates the water level value 15 minutes after the rainfall end signal is generated or the next evaporation calculation cycle ends.

[0113] After obtaining the rainfall, the water level difference is corrected using the following formula to calculate the evaporation:

[0114] E=h1-h2+p

[0115] Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

[0116] For moderate rainfall, there is a special case, that is, the rainfall may continue until the next evaporation calculation cycle. At present, the minimum interval for updating all data, regardless of rainfall, water level, and evaporation, is 5 minutes, that is, the theoretical minimum output is 5 minutes. Therefore, when the evaporation calculation cycle is small, it is likely to cause the rainfall period to cross regions, and the rainfall has not ended or has not stabilized at the end of the evaporation calculation cycle. For this situation, in theory, the water level 15 minutes after the end of the evaporation calculation cycle can be used to replace the water level value 15 minutes after the rainfall end signal is generated for calculation, and the next evaporation calculation cycle uses the measured water level at the start time as the actual starting water level, but when the evaporation calculation cycle is short, the data stability is poor. For this reason, the present invention proposes to set different evaporation data reporting methods for evaporation calculation cycles of different lengths to achieve a balance between data stability and timeliness.

[0117] Specifically, a preset time threshold is set. If the time between the end of the current evaporation calculation cycle and the reporting time of the last evaporation update data is less than the preset time threshold, the last evaporation update data is still reported this time to ensure the stability of the reported data. On the contrary, if the cumulative time of the evaporation unupdated cycle is greater than the preset time threshold, considering the timeliness of the data, the rainfall in the current evaporation calculation cycle is calculated according to the following formula:

[0118] p=h px2 -h p1max

[0119] The water level difference is corrected using the following formula to calculate the evaporation amount:

[0120] E=h1-h2+p

[0121] Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

[0122] Of course, it can also be judged based on the duration of the evaporation calculation cycle. For example, when the evaporation calculation cycle is one day, when the rainfall signal appears across days, each evaporation calculation cycle reports the updated evaporation data. If the evaporation calculation cycle is several hours, only the evaporation data of the last stable period is reported, and the unupdated time is accumulated until the accumulated unupdated time spans days. Although this sacrifices some data timeliness, it is relatively accurate for daily data.

[0123] (5) Heavy rainfall

[0124] In the case of heavy rainfall, the correction of the starting water level is similar to that of moderate rainfall. The difference is that due to the large rainfall, overflow occurs. Once overflow occurs, it is difficult to use water level changes to estimate the rainfall. At this time, a rain gauge must be used. If a rain gauge is used alone to count rainfall, the aforementioned error problem will exist.

[0125] Therefore, in order to effectively count the overflow water volume while taking into account the rainfall measurement accuracy, the present invention proposes a segmented rainfall measurement method based on the 5-minute water level. Specifically, in the case of heavy rainfall, the water level in the level logging well is collected in real time with a collection cycle of 5 minutes. For each collection cycle, the water level in the collected level logging well is compared with the preset overflow water level. If the water level in the level logging well exceeds the overflow water level, the collection cycle is marked as an overflow period, and the rainfall output by the rain gauge is used as the rainfall in the overflow period.

[0126] For the non-overflow period, since the non-overflow period usually occurs at the beginning of rainfall, the rainfall start time can be corrected in combination with the water level balance lag time to calculate the rainfall in the non-overflow period:

[0127]

[0128] In the formula, h px3 Indicates the water level value when overflow begins.

[0129] Combining the rainfall p1 in the non-overflow period and the rainfall p2 in the overflow period, we get the rainfall P=p1+p2 in the case of heavy rainfall. We correct the evaporation to get the evaporation:

[0130] E=h1-h2+p

[0131] Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

[0132] (6) Continuous rainfall

[0133] For rainy areas, the present invention also sets a continuous rainfall type. Continuous rainfall means that the maximum water level after rainfall exceeds the overflow line water level, and the rainfall period covers more than one evaporation calculation cycle. Continuous rainfall has both overflow characteristics and cross-region characteristics. Unlike the cross-region during moderate rainfall, continuous rainfall has overflow characteristics. Therefore, in the next or the next N evaporation calculation cycles, the water level value in the liquid level logging well will be maintained at the overflow water level line, and the water level difference cannot be measured.

[0134] To this end, the present invention sets different evaporation calculation methods for evaporation calculation cycles of different lengths. For a shorter evaporation calculation cycle (such as 4h), based on the evaporation change curve of the evaporation calculation cycle at the beginning of rainfall when there is no rainfall, select the one with the highest similarity from the evaporation change curves of the same period in the past N days, and report the evaporation of that day as the evaporation during continuous rainfall as the reference evaporation. For a longer evaporation calculation cycle (such as one day), firstly, for the evaporation calculation cycle at the beginning of rainfall, use the rainfall calculation method for heavy rainfall, that is, divide it into multiple overflow periods, and use the rainfall output by the rain gauge as the rainfall in the overflow period. For the rainfall in the non-overflow period, use the formula Calculate the rainfall; finally, the total rainfall in the evaporation calculation cycle at the beginning of the rainfall is statistically obtained, and the evaporation-time variation curve when there is no rainfall is drawn. Secondly, due to the water level difference in the evaporation calculation cycle at the end of the rainfall, the evaporation-time variation curve when there is no rainfall in the evaporation calculation cycle at the end of the rainfall is drawn. Thirdly, the evaporation-time variation curve of the study area in an evaporation calculation cycle is fitted by combining the evaporation-time variation curve of the no-rainfall period at the beginning and end of the rainfall, and the rainfall at the beginning of the rainfall. The evaporation calculated according to the curve is used as the evaporation of all evaporation calculation cycles during continuous rainfall. If the no-rainfall period of the two evaporation calculation cycles at the beginning and end of the rainfall cannot cover the entire evaporation calculation cycle, the one with the highest similarity can be selected from the evaporation change curves of the past N days based on the drawn part, and it can be used as a reference to fit the evaporation-time variation curve of the entire evaporation calculation cycle.

[0135] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0136] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0137] These computer program instructions may also be stored in a computer readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0138] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0139] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0140] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for monitoring water surface evaporation with rainfall compensation, characterized in that: The water surface evaporation monitoring method The following steps are involved: S1, design a water level balance test according to the connection structure of the liquid level logging well and the evaporation dish to obtain the water level balance lag time between the evaporation dish and the liquid level logging well; S2, regularly collect the water level in the liquid level logging well, and store the collected water level value and the corresponding collection time in the water level database; use a rain gauge to regularly monitor whether rainfall occurs and the corresponding rainfall amount; S3, in a new evaporation calculation cycle, using the water level balance lag time to correct the current evaporation calculation cycle to obtain a corrected evaporation calculation cycle, and fitting to obtain a curve of the change of the water level over time in the corrected evaporation calculation cycle; S4, judging the rainfall type in combination with the rainfall signal fed back by the rain gauge or the water level variation curve over time, the rainfall types include no rainfall, light rainfall, moderate rainfall and heavy rainfall; wherein, light rainfall means that no rainfall signal fed back by the rain gauge is received, but the water level variation curve over time during the evaporation calculation period reflects rainfall; moderate rainfall means that the rainfall signal fed back by the rain gauge is received and the maximum water level value does not exceed the overflow line water level; heavy rainfall means that the maximum water level value after rainfall exceeds the overflow line water level and the rainfall period is within the evaporation calculation period; S5, in the case of no rainfall, the evaporation amount of the current evaporation amount calculation period is calculated by combining the water level change value of the evaporation amount calculation period calculated by combining the water level balance lag time; In the case of slight rainfall, the evaporation of the current evaporation calculation period is predicted by combining the evaporation type of the study area, the evaporation change curve of the previous N evaporation calculation periods, and the water level change curve of the revised evaporation calculation period over time; In the case of moderate rainfall, the rainfall start time is corrected in combination with the water level balance lag time to calculate the rainfall in the current evaporation calculation period; the water level change value in the evaporation calculation period is corrected using the calculated rainfall to calculate the evaporation in the current evaporation calculation period; In the case of heavy rainfall, the overflow period is selected according to the water level. For each overflow period, the rainfall output by the rain gauge is used as the rainfall in the overflow period. The rainfall start time is corrected in combination with the water level balance lag time, and the rainfall in the non-overflow period is calculated in combination with the water level value. The total rainfall is used to correct the water level change value of the evaporation calculation period, and the evaporation of the current evaporation calculation period is calculated.

2. The method for monitoring water surface evaporation with rainfall compensation according to claim 1, characterized in that: When receiving the rainfall change signal fed back by the rain gauge, the first rainfall change signal is taken as the rainfall start signal, and the last rainfall change signal is taken as the rainfall end signal; the last rainfall change signal means that there is no new rainfall change signal within a preset time range after the rainfall change signal; the time between the rainfall start signal and the corresponding rainfall end signal is taken as a rainfall period.

3. The method for monitoring water surface evaporation with rainfall compensation according to claim 1, characterized in that: Combined with the rainfall signal fed back by the rain gauge or the water level change curve over time, the process of determining the rainfall type includes the following steps: A1, determine whether the rainfall change signal fed back by the rain gauge is received during the evaporation calculation period, if yes, it is determined that there is rainfall, then further determine whether the rainfall type is medium rainfall or heavy rainfall according to whether the real-time water level reaches the overflow water level, and end the process, otherwise, go to step A2; A2, divide the evaporation calculation period into several statistical periods, and draw the historical evaporation-time curve based on the historical evaporation data when there is no rainfall, taking a single statistical period as the basic time unit; A3, analyze the historical evaporation-time curve to obtain the evaporation proportion law of different statistical periods within an evaporation calculation cycle or the evaporation range of each statistical period when there is no rainfall; A4, fitting to obtain the water level variation curve over time of the modified evaporation calculation period, calculating and drawing the evaporation-time curve of the current evaporation calculation period, judging whether each statistical period conforms to the evaporation proportion law or the corresponding evaporation interval, if all conform, judging that there is no rainfall, and ending the process, otherwise, marking the non-conforming statistical period as an abnormal period, and proceeding to step A5; A5, with 5 minutes as an analysis cycle, draws the water level change curve during the abnormal period; judges whether rainfall occurs in the current analysis cycle based on the water level change slope of the adjacent analysis cycle. If rainfall occurs, it is determined that light rainfall occurs in the current evaporation calculation cycle.

4. The method for monitoring water surface evaporation with rainfall compensation according to claim 2, characterized in that: In step A4, for each analysis cycle, water level values ​​are collected 10 times with a period of 30 seconds, and the average value of the 10 water level values ​​is taken as the water level value of the current analysis cycle.

5. The method for monitoring water surface evaporation with rainfall compensation according to claim 1, characterized in that: For the case of no rainfall, the evaporation calculation formula is: E=h1-h2 Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

6. The method for monitoring water surface evaporation with rainfall compensation according to claim 1, characterized in that: For the case of light rainfall, the process of predicting the evaporation of the current evaporation calculation period includes the following steps: B1, collect the historical evaporation change curves of different study areas, analyze the evaporation change curves of each study area when there is no rainfall, manually mark the evaporation type according to the evaporation ratio of the time period, and construct the first data set; B2, using the first constructed data set to train the convolutional neural network to obtain an evaporation type recognition model; B3, import the historical evaporation change curve of the study area into the trained evaporation type recognition model, and output the corresponding evaporation type of the study area; B4, according to the evaporation type of the current study area, the evaporation change curve of the study area with the same evaporation type without rainfall is imported into the LSTM network for training to obtain the evaporation prediction model corresponding to the study area; B5, the evaporation of the first N evaporation calculation cycles is calculated according to the water level change curve of the first N evaporation calculation cycles, and the evaporation is imported into the trained evaporation prediction model to predict the evaporation of the current evaporation calculation cycle.

7. The method for monitoring water surface evaporation with rainfall compensation according to claim 1, characterized in that: For moderate rainfall, the calculation process of rainfall in the current evaporation calculation period includes the following steps: C1, if the rainfall end signal occurs in the current evaporation calculation cycle, the rainfall in the current evaporation calculation cycle is calculated using the following formula: In the formula, h px1 Indicates the water level value X hours before the rainfall start signal; h p1max Indicates the highest water level value within 1 hour before the rainfall signal; h px2 Indicates the water level value for X periods of time after the rainfall end signal is generated or the next evaporation calculation cycle ends; go to step B4; otherwise, go to step B2; C2, determine whether the accumulated duration of the evaporation amount not updated period is greater than the preset duration threshold, if so, proceed to step B3, otherwise, report the evaporation amount of the last stable period, and the evaporation amount not updated period is increased by one; C3, calculate the rainfall in the current evaporation calculation period according to the following formula: p=h px2 -h p1max ; C4, the evaporation is calculated using the following formula: E=h1-h2+p Wherein, h1 represents the average water level collected at the start time of the evaporation calculation period; h2 represents the average water level collected at the end time of the evaporation calculation period.

8. The method for monitoring water surface evaporation with rainfall compensation according to claim 1, characterized in that: In case of heavy rainfall, the water level in the level logging well is collected in real time with a collection cycle of 5 minutes; For each collection period, the water level in the collected level logging well is compared with the preset overflow water level. If the water level in the level logging well exceeds the overflow water level, the collection period is marked as the overflow period, and the rainfall output by the rain gauge is used as the rainfall in this period; For the non-overflow period, the rainfall start time is corrected by combining the water level balance lag time, and the rainfall in the non-overflow period is calculated: In the formula, h px3 Indicates the water level value when overflow begins; Combining the rainfall p1 during the non-overflow period and the rainfall p2 during the overflow period, the rainfall under heavy rainfall conditions is obtained as P = p1 + p 2， Correct the evaporation to get the evaporation: E = h1 - h2 + p; In the formula, h 11 h2 represents the average water level collected at the start time of the evaporation calculation cycle; h3 represents the average water level collected at the end time of the evaporation calculation cycle.

9. The method for monitoring water surface evaporation with rainfall compensation according to claim 1, characterized in that: The rainfall type includes continuous rainfall; continuous rainfall means that the maximum water level after rainfall exceeds the overflow line water level, and the rainfall period covers more than one evaporation calculation cycle; the evaporation monitoring process during continuous rainfall includes the following steps: D1, determine whether the duration of the evaporation calculation cycle is less than a preset duration threshold, if so, proceed to step D2; D2, based on the evaporation change curve of the evaporation calculation period at the beginning of rainfall when there is no rainfall, select the one with the highest similarity from the evaporation change curves of the same period in the past N days, and report the evaporation of the selected evaporation change curve at the same time on the same day as the reference evaporation of each evaporation calculation period during continuous rainfall; end the process; D3, for the evaporation calculation cycle at the beginning of rainfall, the rainfall period is divided into multiple overflow periods, and the rainfall output by the rain gauge is used as the rainfall in the overflow period. For the rainfall in the non-overflow period, the formula is used. Calculate the rainfall; obtain the total rainfall in the evaporation calculation period from the beginning of rainfall, and draw the evaporation-time variation curve when there is no rainfall; According to the water level value of the evaporation calculation period at the end of rainfall, the evaporation-time variation curve when there is no rainfall in the evaporation calculation period at the end of rainfall is drawn; Combining the evaporation change curves over time in the rainless periods of the two evaporation calculation cycles at the beginning and end of rainfall, as well as the rainfall at the beginning of rainfall, a curve of evaporation change over time in the study area in one evaporation calculation cycle was fitted. The evaporation calculated based on this curve was used as the evaporation for all evaporation calculation cycles during continuous rainfall.

10. The method for monitoring water surface evaporation with rainfall compensation according to claim 9, characterized in that: If the rainfall-free periods in the two evaporation calculation cycles at the beginning and end of rainfall cannot cover the entire evaporation calculation cycle, the one with the highest similarity is selected from the evaporation change curves of the past N days based on the drawn part, and it is used as a reference to fit the evaporation-time change curve of the entire evaporation calculation cycle.

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