Solar altitude correction method and device for spectral reflectivity sensor and storage medium
By calculating and vector decomposing the proportion of sky light, the reflectivity formula after sun altitude correction is derived, which solves the problem of low measurement accuracy of sensors when sun altitude changes, and improves the utilization rate and working efficiency of the equipment.
Patent Information
- Application Number
- CN202411627711.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-14
- Publication Date
- 2025-02-18
AI Technical Summary
When measuring the reflectivity of vegetation, the existing spectral reflectivity sensors have low accuracy in reflectivity measurement due to changes in the sun's height, and the equipment is low in utilization and low working efficiency.
By calculating the proportion of direct sunlight and scattered sky light in the sky light received by the sensor, and performing vector decomposition, the reflectance formula after sun altitude correction is derived to achieve correction of the sensor measurement results.
It improves the accuracy of sensor measurements, broadens the time range for sensors to work in a day, and improves the utilization rate of equipment and the work efficiency of staff.
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Figure CN119470353A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of optical remote sensing, and in particular relates to a method, a device and a storage medium for spectral reflectance sensor solar altitude correction. Background Art
[0002] The rapid and accurate acquisition of vegetation growth information is of great significance for its growth and development regulation, so the use of spectral sensors to measure reflectivity has been widely used in production. The vegetation canopy is similar to the Lambertian surface, and its reflected light is not affected by the altitude of the sun. However, the direct sunlight in the sky light changes with the altitude of the sun, and the incident angle of the sensor optical window also changes, so that the transmittance is affected by the altitude of the sun, which ultimately affects the accuracy of the reflectivity measurement.
[0003] In order to reduce the impact of the sun's altitude on sensor measurements, the optical window of the sensor that receives sky light is often installed with a cosine corrector. The material of the cosine corrector is usually opal glass, polytetrafluoroethylene, etc. The light passing through the cosine corrector becomes diffuse light and has no directionality. However, in actual applications, people have found that the sensor equipped with a cosine corrector is still affected by the sun's altitude when working. Specifically, the reflectivity decreases with the increase of the sun's altitude angle, and the reflectivity value is the smallest around noon. The reflectivity measured throughout the day shows a "U"-shaped change trend. The sun's altitude changes slowly around noon, and the measured reflectivity is relatively stable. Therefore, people often measure the reflectivity of vegetation around noon, such as 10:00-14:00, 11:00-13:00, etc. However, if the measurement is only around noon, the working period of the day is short, resulting in low equipment utilization and low work efficiency. In addition, the high temperature at noon in summer also poses a great challenge to field work during this period. Summary of the invention
[0004] In response to the problems existing in the prior art mentioned in the background technology, the present invention provides a spectral reflectance sensor solar altitude correction method, equipment and storage medium. This method can be used to perform measurements throughout the day, has good applicability, can improve measurement accuracy, and improve equipment utilization.
[0005] Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:
[0006] A sun altitude correction method for a spectral reflectance sensor calculates the spectral reflectance based on a vegetation spectral reflectance sensor, estimates the proportion of direct sunlight and the proportion of sky scattered light in the sky light received by the sensor, and finally calculates the reflectance after sun altitude correction.
[0007] Preferably, the specific content of calculating the spectral reflectance based on the vegetation spectral reflectance sensor is:
[0008] First, a vegetation spectral reflectance sensor is used to measure the intensity of sky light and light reflected from ground objects;
[0009] The spectral reflectance is the ratio of the reflected light energy of a specific band reflected by the ground object to the incident light energy of the ground object in the same band; the spectral reflectance measured by the sensor is:
[0010]
[0011] Among them, ρ λ is the reflectivity of the λ band measured by the sensor, U D U is the voltage value obtained by measuring the reflected light from the ground through the sensor. U It is the voltage value measured by the sensor when the incident light from the sky is received by the ground object.
[0012] Preferably, the proportion of direct sunlight and the proportion of scattered sky light in the sky light received by the sensor are estimated, specifically:
[0013] The proportion of direct sunlight PD is expressed as:
[0014] PD = sin(0.7128θ),
[0015] The proportion of scattered light in the sky, PS, is expressed as:
[0016] PS = 1-sin(0.7128θ),
[0017] Here, θ is the altitude of the sun.
[0018] As a preferred method, the specific content of the final calculation of the reflectivity after the sun altitude correction is:
[0019] U measured by the sensor U It is decomposed into two parts, one part is converted from direct sunlight, represented by U U PD, the other part is converted from the sky scattered light, expressed as U U PS;
[0020] The direct sunlight is vector-decomposed, one part of which propagates vertically downward and enters the sensor perpendicular to the optical window of the sensor. U PD represents the intensity of this part of light, and the other part is decomposed into horizontal propagation, and this part of light will not enter the sensor;
[0021] Based on the vector decomposition of direct sunlight, the voltage value U corresponding to direct sunlight is theoretically solar It is expressed as:
[0022]
[0023] Therefore, the reflectivity ρ after solar altitude correction isλ,θ It is expressed as formula (1), and after rearrangement, it can be obtained as formula (2);
[0024]
[0025] An electronic device comprises a processor and a memory storing a computer program, wherein the processor implements the steps of the above-mentioned method for calibrating the solar altitude of a spectral reflectance sensor when executing the computer program.
[0026] A computer-readable storage medium stores a computer program or instruction, which, when executed by a processor, implements the steps of the above-mentioned method for calibrating the solar altitude of a spectral reflectance sensor. Advantageous effects: Compared with the prior art, the present invention has the following advantages:
[0027] The present invention decomposes the optical signal measured by the sensor according to the source of light and the transmission path of the light, and derives a solar altitude correction method for the spectral reflectance sensor. The correction method has strong theoretical basis and good applicability, improves the accuracy of sensor measurement, broadens the working time range of the sensor in a day, facilitates the measurement work, improves the utilization rate of the sensor, and improves the work efficiency of the staff during measurement. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 is a schematic diagram of a single-channel spectral reflectance sensor;
[0029] Figure 2 It is a schematic diagram of the decomposition of direct sunlight vector of the present invention;
[0030] Figure 3 is a schematic diagram of the overall structure of the spectral reflectance sensor according to an embodiment of the present invention;
[0031] Figure 4 It is a schematic diagram of the reflectivity of bermudagrass lawn measured by the sensor of an embodiment of the present invention throughout the day and the reflectivity after correction for the sun altitude. DETAILED DESCRIPTION
[0032] The present invention is further illustrated below in conjunction with specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.
[0033] Example 1
[0034] Use as Figure 3The vegetation canopy reflectance sensor shown measures the all-day reflectance of bermudagrass turf. The sensor has two bands, 710nm and 870nm. The measurement location is Huaiyin Normal University. The measurement date is July 31, 2024. The measurement time range is 8:00-17:00. It is measured once every minute, and the sun altitude is recorded synchronously with the measurement.
[0035] The optical window at the top of the sensor is used to receive sky light, and the optical window at the bottom of the sensor is used to receive light reflected from ground objects. Figure 1 shown.
[0036] The solar altitude calibration method for a spectral reflectance sensor provided in this embodiment includes the following steps:
[0037] S1: Calculate spectral reflectance based on vegetation spectral reflectance sensor;
[0038] First, a vegetation spectral reflectance sensor is used to measure the intensity of sky light and light reflected from ground objects;
[0039] When the sensor is working, the optical window is in a horizontal state. The spectral reflectance can be expressed as the ratio of the reflected light energy of a specific band reflected by the ground object to the incident light energy of the ground object in this band. The spectral reflectance measured by the sensor is:
[0040]
[0041] Among them, ρ λ is the reflectivity of the λ band measured by the sensor, U D U is the voltage value obtained by measuring the reflected light from the ground through the sensor. U It is the voltage value measured by the sensor when the incident light from the sky is received by the ground object.
[0042] S2: Estimate the proportion of direct sunlight and the proportion of scattered sky light in the sky light received by the sensor;
[0043] The canopy of vegetation is similar to the Lambertian surface, and its reflected light is diffuse light, non-directional, and unaffected by the height of the sun. The sky light received by the vegetation canopy includes direct light from the sun and scattered light from the sky. Direct light is directional. When the height of the sun increases, the incident angle of direct light from the sun on the optical window of the sensor decreases, and the light energy transmittance increases, making the light energy transmittance of the sensor different at different sun heights, so that the vegetation reflectance measured by the sensor throughout the day changes in a "U" shape, and the measurement accuracy is not high.
[0044] On a sunny day near noon, the proportion of direct sunlight to sky light can reach 80-90%, while when the sun is on the horizon, that is, when the sun's altitude is 0, the sky light is all scattered light, and the proportion of direct sunlight is 0. Based on the changing characteristics of the proportion of direct light and scattered light in the sky light, the sine function can be used to represent it, sin(a×90°)=0.9, sin(a×0°)=0, and a=0.7128.
[0045] The proportion of direct sunlight PD can be expressed as:
[0046] PD = sin(0.7128θ),
[0047] Correspondingly, the proportion of scattered light in the sky PS can be expressed as:
[0048] PS = 1-sin(0.7128θ),
[0049] Here, θ is the altitude of the sun.
[0050] S3: Finally, calculate the reflectivity after sun altitude correction.
[0051] Sensor measured U U It can be decomposed into two parts, one part is converted from direct sunlight, expressed as U U PD, the other part is converted from the sky scattered light, expressed as U U PS.
[0052] The direct sunlight is vector-decomposed, one part of which propagates vertically downward and enters the sensor perpendicular to the optical window of the sensor. U PD represents the intensity of this part of light, and the other part is decomposed into horizontal propagation, which will not enter the sensor.
[0053] Based on the vector decomposition of direct sunlight, the voltage value U corresponding to direct sunlight is theoretically solar It can be expressed as:
[0054]
[0055] Therefore, the reflectivity after solar altitude correction is ρ λ,θ It can be expressed as formula (1), and after rearrangement, it can be expressed as formula (2).
[0056]
[0057] The measured reflectivity ρ 710 and ρ 870 Formula (2) is used to calculate the reflectivity after solar altitude correction. The results are as follows: Figure 4As shown, in the 710nm band, the coefficient of variation CV of the all-day reflectivity measured by the sensor is 10.86%, which is reduced to 2.93% after solar altitude correction. In the 870nm band, the coefficient of variation CV of the all-day reflectivity measured by the sensor is 9.69%, which is reduced to 1.53% after solar altitude correction. It can be seen that after solar altitude correction, the all-day reflectivity is more stable and is less affected by the solar altitude.
[0058] Example 2
[0059] An electronic device comprises a processor and a memory storing a computer program. When the processor executes the computer program, the steps of the above-mentioned method for calibrating the solar altitude of a spectral reflectance sensor are implemented.
[0060] The processor may be a CPU (Central Processing Unit), a general-purpose processor, a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. It may implement or execute various exemplary logic blocks, modules and circuits described in conjunction with the disclosure of this application. The processor may also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.
[0061] The memory can be a ROM (Read Only Memory) or other types of static storage devices that can store static information and instructions, a RAM (Random Access Memory) or other types of dynamic storage devices that can store information and instructions, or an EEPROM (Electrically Erasable Programmable Read Only Memory), a CD-ROM (Compact Disc Read Only Memory) or other optical disk storage, optical disk storage (including compressed optical disk, laser disc, optical disk, digital versatile disc, Blu-ray disc, etc.), a magnetic disk storage medium or other magnetic storage device, or any other medium that can be used to carry or store the desired computer program in the form of instructions or data structures and can be accessed by a computer, but is not limited to these.
[0062] Example 3
[0063] A computer-readable storage medium stores a computer program or instruction, which, when executed by a processor, implements the steps of the above-mentioned method for calibrating the solar altitude of a spectral reflectance sensor.
[0064] The computer-readable storage media provided herein include, but are not limited to, any type of disk (including floppy disk, hard disk, optical disk, CD-ROM, and magneto-optical disk), ROM, RAM, EPROM (Erasable Programmable Read-Only Memory), EEPROM, flash memory, magnetic card or optical card. In other words, the readable medium includes any medium that can store or transmit information in a readable form by a device (e.g., a computer).
[0065] In this embodiment, a VCR vegetation reflectance sensor is used, and the MCU (microcontroller unit) of the sensor is MSP430I2041, which has built-in storage.
[0066] The present invention is not limited to sensors, and the reflectivity can be directly measured by sensors. The present invention improves the accuracy of sensor measurement, broadens the working time range of the sensor in a day, facilitates the measurement work, and improves the utilization rate of the sensor and the work efficiency of the staff during measurement.
[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.
Claims
1. A method for calibrating the sun's altitude of a spectral reflectance sensor, characterized in that: The spectral reflectance is calculated based on the vegetation spectral reflectance sensor, the proportion of direct sunlight and the proportion of sky scattered light in the sky light received by the sensor are estimated, and finally the reflectance after sun altitude correction is calculated.
2. The method for calibrating the sun's altitude of a spectral reflectance sensor according to claim 1, characterized in that: The specific content of calculating spectral reflectance based on vegetation spectral reflectance sensor is: First, a vegetation spectral reflectance sensor is used to measure the intensity of sky light and light reflected from ground objects; The spectral reflectance is the ratio of the reflected light energy of a specific band reflected by the ground object to the incident light energy of the ground object in the same band; the spectral reflectance measured by the sensor is: Among them, ρ λ is the reflectivity of the λ band measured by the sensor, U D U is the voltage value obtained by measuring the reflected light from the ground through the sensor. U It is the voltage value measured by the sensor when the incident light from the sky is received by the ground object.
3. The method for calibrating the sun's altitude of a spectral reflectance sensor according to claim 2, characterized in that: Estimate the proportion of direct sunlight and diffuse sky light in the sky light received by the sensor. The specific contents are: The proportion of direct sunlight PD is expressed as: PD = sin(0.7128θ), The proportion of scattered light in the sky, PS, is expressed as: PS = 1-sin(0.7128θ), Here, θ is the altitude of the sun.
4. The method for calibrating the sun's altitude of a spectral reflectance sensor according to claim 3, characterized in that: Finally, the specific content of calculating the reflectivity after solar altitude correction is: U measured by the sensor U It is decomposed into two parts, one part is converted from direct sunlight, represented by U U PD, the other part is converted from the sky scattered light, expressed as U U PS; The direct sunlight is vector-decomposed, one part of which propagates vertically downward and enters the sensor perpendicular to the optical window of the sensor. U PD represents the intensity of this part of light, and the other part is decomposed into horizontal propagation, and this part of light will not enter the sensor; Based on the vector decomposition of direct sunlight, the voltage value U corresponding to direct sunlight is theoretically solar It is expressed as: Therefore, the reflectivity ρ after solar altitude correction is λ,θ It is expressed as formula (1), and after rearrangement, it can be obtained as formula (2); 5. An electronic device comprising a processor and a memory storing a computer program, characterized in that: When the processor executes the computer program, the steps of the method for calibrating the solar altitude of a spectral reflectance sensor according to any one of claims 1 to 4 are implemented.
6. A computer-readable storage medium having a computer program or instruction stored thereon, characterized in that: When the computer program or instruction is executed by a processor, the steps of the method for sun altitude correction of a spectral reflectance sensor according to any one of claims 1 to 4 are implemented.