High-altitude balloon land recovery method based on sea and land wind

Abstract

The invention relates to a high-altitude balloon land recovery method based on sea and land wind, and relates to the technical field of high-altitude balloons. The method comprises the steps that wind field information is collected in advance, after the high-altitude balloon is released and released from a flying spot, balloon height information is collected in real time, whether the high-altitude balloon reaches the preset floating height or not is judged according to the balloon height information, and meanwhile data collection is conducted in the process that the high-altitude balloon is blown to the ocean by land wind; and the to-be-recycled part is separated from the high-altitude balloon, blown to the land by the sea wind and finally falls into the recycling position. The releasing personnel can wait at the recovery position, land recovery is achieved, the releasing personnel do not need to conduct offshore recovery, the recovery pressure is effectively relieved, the recovery difficulty is lowered, and the problem that an existing high-altitude balloon load recovery mode is high in recovery difficulty is solved.

Description

Technical Field

[0001] The invention relates to the technical field of high-altitude balloons, and in particular to a land recovery method for high-altitude balloons based on sea and land breezes. Background Art

[0002] Meteorological and environmental data collection in coastal areas and coastal zones is very important for understanding natural conditions, dynamic changes and their interactions with human activities.

[0003] The existing technology often uses high-altitude balloons to collect common coastal and coastal environmental information. However, high-altitude balloons fly toward the sea and fall into the sea when landing. The high-value instruments and equipment contained in the balloon's payload and the large amount of rare in-situ data collected are easily lost, and the recovery at sea requires a lot of manpower, ships and other costs, resulting in high recovery costs for high-altitude balloons.

[0004] With respect to the above-mentioned related technologies, there is a problem that the existing high-altitude balloon payload recovery method is difficult to recover. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a method for recovering a high-altitude balloon on land based on sea and land breezes, aiming to solve the problem of high difficulty in recovering the existing high-altitude balloon payload recovery methods.

[0006] The present application provides a method for recovering a high-altitude balloon on land based on sea and land breezes, which adopts the following technical solution: A method for recovering a high-altitude balloon on land based on sea and land breezes, comprising:

[0007] Collecting wind field information in advance, wherein the wind field information includes the wind time, direction, speed of land wind, wind time, direction and speed of sea wind;

[0008] Determine the launch point and release the high-altitude balloon;

[0009] After the balloon is released, the balloon altitude information is collected in real time, and the balloon altitude information is used as a basis to determine whether the predetermined floating altitude has been reached;

[0010] When the high-altitude balloon rises to a predetermined floating height, the part to be recovered is released.

[0011] Optionally, the launching point is set on land, and the high-altitude balloon will pass through the low-altitude area and enter the high-altitude area during the process of being blown from land to the ocean, and finally rise to a predetermined floating height.

[0012] Optionally, the distance from the release point to the ocean is greater than or equal to 100 kilometers;

[0013] And the distance from the release point to the ocean is less than or equal to 200 kilometers.

[0014] Optionally, the wind speed of the land breeze is greater than or equal to 2 m / s;

[0015] And the wind speed of the land breeze is less than or equal to 5 meters per second.

[0016] Optionally, the distance from the predetermined floating altitude to the ground is greater than or equal to 18 kilometers;

[0017] And the distance from the predetermined floating altitude to the ground is less than or equal to 22 kilometers.

[0018] Optionally, when the object to be recovered lands in the low-altitude area, the distance between the object to be recovered and the sea level is greater than or equal to 2 kilometers.

[0019] Optionally, when the to-be-recovered part lands in the low-altitude area, the horizontal distance between the to-be-recovered part and the recovery position is greater than or equal to 5 kilometers;

[0020] And the horizontal distance from the to-be-recovered part to the recovery location is less than or equal to 6 kilometers.

[0021] Optionally, the to-be-recovered component includes a parachute and a data acquisition component, and the data acquisition component is used to collect and store data information;

[0022] When the to-be-recovered component is separated from the parachute, the parachute opens to slow down the descent speed of the data acquisition component.

[0023] Optionally, the vertical falling speed of the data acquisition component is greater than or equal to 1.5 m / s;

[0024] And the vertical falling speed of the data acquisition component is less than or equal to 2.5 meters per second.

[0025] Optionally, the wind speed of the sea breeze is greater than or equal to 5 m / s;

[0026] And the wind speed of the sea breeze is less than or equal to 6 meters per second.

[0027] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0028] Conduct preliminary wind field information collection, determine the launch point and release the high-altitude balloon. After the launch, collect the balloon altitude information in real time, and use the balloon altitude information as the basis to determine whether the predetermined floating altitude has been reached. At the same time, data will be collected while the high-altitude balloon is being blown toward the ocean by the land breeze. When the high-altitude balloon rises to the predetermined floating altitude, the recovery component is released, separated from the high-altitude balloon, blown toward the land by the sea breeze, and finally falls into the recovery position.

[0029] The launch personnel can wait at the recovery location to realize land recovery. The launch personnel do not need to conduct sea recovery, which effectively reduces the recovery pressure and difficulty, and solves the problem of high recovery difficulty of existing high-altitude balloon payload recovery methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 Schematic diagram of the flight route of the high-altitude balloon and the object to be recovered in the high-altitude balloon land recovery method based on sea and land winds in the embodiment of the present application;

[0032] Figure 2 It is a flow chart of the high-altitude balloon land recovery method based on sea and land breezes in an embodiment of the present application.

[0033] Description of reference numerals:

[0034] 1. High-altitude balloon; 11. Parts to be recovered; 111. Parachute; 112. Data collection parts; 2. High-altitude wind; 3. Land breeze; 4. Sea breeze; 5. Route with the lowest wind speed; 6. Route with the highest wind speed; 7. Release point; 8. Predetermined floating height; 9. Recovery location; 10. Land; 12. Ocean; 13. High-altitude area; 14. Low-altitude area. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The present application is further described in detail below in conjunction with the accompanying drawings.

[0037] The embodiment of the present application discloses a method for recovering a high-altitude balloon on land based on sea and land breezes.

[0038] like Figure 1 and Figure 2 As shown, a method for recovering a high-altitude balloon on land based on sea and land breezes comprises the following steps:

[0039] S100, collecting wind field information in advance, wherein the wind field information includes information on wind time, direction, and speed of land breeze, wind time, direction, and speed of sea breeze, wind time, and wind direction of sea breeze, and wind speed of sea breeze.

[0040] Specifically, the sea and land breeze is a local wind with daily periodicity that occurs in offshore and coastal areas, and is generated due to the difference in heat capacity between the land 10 and the ocean 12. The sea and land breeze consists of two parts, the sea breeze 4 and the land breeze 3. The wind direction of the land breeze 3 blows from the land 10 to the ocean 12, while the wind direction of the sea breeze 4 blows from the ocean 12 to the land 10. The sea breeze 4 blows from the ocean 12 to the land 10 during the day, usually starting in the morning until the evening, and the wind reaches its strongest in the afternoon.

[0041] The aerial area is divided into a low-altitude area 14 and a high-altitude area 13. The height from the low-altitude area 14 to the ground is less than the height from the high-altitude area 13 to the ground. The distance from the low-altitude area 14 to the ground is 0-2 kilometers (km), and the distance from the high-altitude area 13 to the ground is more than 2km.

[0042] The wind located in the low-altitude area 14 is the low-altitude wind (i.e., sea and land breeze), and the wind located in the high-altitude area 13 is the high-altitude wind 2.

[0043] The low-altitude wind includes the sea breeze 4 and the land breeze 3 , and the wind direction of the land breeze 3 and the high-altitude wind 2 is the same, both blowing from the land 10 to the ocean 12 , while the wind direction of the sea breeze 4 is blowing from the ocean 12 to the land 10 .

[0044] The wind speed of the low-altitude wind is greater than or equal to 2 meters / second, and the wind speed of the low-altitude wind is less than or equal to 5 meters / second. The wind speed of the high-altitude wind 2 decreases significantly with decreasing altitude. The wind speed of the high-altitude wind 2 is greater than or equal to 15 meters / second, and the wind speed of the high-altitude wind 2 is less than or equal to 40 meters / second.

[0045] The wind field information includes the wind time, direction, and speed of land breeze 3 , the wind time, direction, and speed of sea breeze 4 , the wind time, direction, and speed of upper wind 2 , and the wind direction, direction, and speed of upper wind 2 .

[0046] Before releasing and recovering the high-altitude balloon 1, the wind field in the area on that day should be collected, and the wind speed, wind time and wind direction information of the sea breeze 4, land breeze 3 and high-altitude wind 2 on that day should be calculated. The release point 7 of the high-altitude balloon 1, the release time and the recovery time and recovery position 9 of the recovered object 11 should be calculated based on the wind field information to improve the accuracy of the recovered object 11 landing at the release point 7, reduce the recovery pressure of the release personnel, and reduce the difficulty of recovery.

[0047] S200. Determine the launch point and release the high-altitude balloon.

[0048] Specifically, after the high-altitude balloon 1 is released from the release point 7, it will gradually rise upward, and the high-altitude balloon 1 will enter the high-altitude area 13 from the low-altitude area 14. When the high-altitude balloon 1 is in the low-altitude area 14, it will be affected by the land breeze 3 and move towards the direction of the ocean 12. After the high-altitude balloon 1 enters the high-altitude area 13, it will be affected by the high-altitude wind 2 and continue to move towards the direction of the ocean 12. The high-altitude balloon 1 will eventually rise to the predetermined floating height 8. The predetermined floating height 8 refers to the designated height at which the high-altitude balloon 1 rises, and the height refers to the distance from the position of the high-altitude balloon 1 to the sea level. The predetermined floating height 8 of the high-altitude balloon 1 is greater than or equal to 18 kilometers, and the predetermined floating height 8 of the high-altitude balloon 1 is less than or equal to 22 kilometers. The predetermined floating height 8 can be adjusted according to actual test requirements.

[0049] Since the wind speeds of the low-altitude wind and the high-altitude wind 2 are not constant, the launching point 7 of the high-altitude balloon 1 needs to be determined according to the wind speeds of the low-altitude wind and the high-altitude wind 2 .

[0050] The selection of the launch point 7 is deep inland. When the land wind 3 has the minimum wind speed of 2 m / s, in order to allow the recovered component 11 to successfully fall to the ground, the distance between the launch point 7 and the ocean 12 is the shortest at this time, and the distance between the launch point 7 and the ocean 12 is 100 km. When the high-altitude balloon 1 rises to the highest point, i.e., the predetermined floating height 8, the wind speed of the high-altitude wind 2 at the height of the high-altitude balloon 1 is 15 m / s.

[0051] When the land breeze 3 has a maximum wind speed of 5 m / s, the distance between the launch point 7 and the ocean 12 is the farthest, which is 200 km. At this time, when the high-altitude balloon 1 rises to the highest point, i.e., the predetermined floating height 8, the wind speed of the high-altitude wind 2 at the height of the high-altitude balloon 1 is 40 m / s.

[0052] The specific release point 7 is adjusted according to the actual wind speed of the day.

[0053] The high-altitude balloon 1 can continuously collect data since it is released.

[0054] The high-altitude balloon 1 includes a buoyancy bag, in which buoyancy gas is stored. The buoyancy gas is one of helium or hydrogen, and the buoyancy gas drives the high-altitude balloon 1 to float upward.

[0055] Furthermore, since the high-altitude balloon 1 needs to collect data in the air for a long time, the volume of the buoyancy gas in the buoyancy bag may be compressed due to temperature changes, making the buoyancy insufficient to support the high-altitude balloon 1 to maintain its current altitude.

[0056] Therefore, the high-altitude balloon 1 also includes a ballast adjustment system, which can adjust the height of the high-altitude balloon 1. The ballast adjustment system includes a storage cabin and ballast, the buoyancy airbag is arranged on the storage cabin, a storage space is formed in the storage cabin, and ballast is stored in the storage space. A discharge port is arranged on the side of the storage cabin away from the buoyancy airbag, and an opening and closing plate is arranged on the discharge port.

[0057] S300: After the balloon is released, the balloon altitude information is collected in real time, and whether the predetermined altitude is reached is determined based on the balloon altitude information.

[0058] Specifically, the balloon altitude information refers to the distance from the current position to the sea level after the high-altitude balloon 1 is released.

[0059] The ballast regulating system also includes a controller and an altimeter. The controller is communicatively connected with a remote control center, and the controller can receive control signals from the remote control center.

[0060] The altimeter is arranged on the accommodation cabin, and the altimeter can record the current balloon altitude information of the high-altitude balloon 1, and the altimeter is electrically connected to the controller. Through the controller, the remote control center can obtain the current balloon altitude information of the high-altitude balloon 1.

[0061] The controller is electrically connected to the opening and closing plate, and the controller can control the opening and closing of the opening and closing plate. When the opening and closing plate is opened, the ballast can be discharged through the discharge port.

[0062] When the remote control center learns that the altitude of the high-altitude balloon 1 has dropped or is no longer within the range of the predetermined floating altitude 8, the remote control center can send a control signal to the controller to operate the opening and closing plate to open, thereby discharging part of the ballast in the accommodation space to reduce the weight of the high-altitude balloon 1 so that the high-altitude balloon 1 can be stabilized at the predetermined floating altitude 8 again for data collection.

[0063] S400, when the high-altitude balloon 1 rises to a predetermined floating height 8, the to-be-recovered component 11 is released.

[0064] Specifically, the operator of the remote control center can remotely control the high-altitude balloon 1 to release the part 11 to be recovered.

[0065] The high-altitude balloon 1 includes a wind speed sensor, which can obtain wind speed information at the current location of the high-altitude balloon 1. The wind speed information includes wind direction information and wind speed information. The wind speed sensor is electrically connected to the controller, and the wind speed sensor can upload the wind speed information to the remote control center through the controller.

[0066] The high-altitude balloon 1 includes a limiter, which is arranged on the accommodation cabin and is electrically connected to the controller. The part to be recovered 11 is detachably arranged on the limiter. The remote control center can remotely control the limiter to release the part to be recovered 11 from the restraint of the limiter.

[0067] In one implementation of the embodiment of the present application, the limiting member is an electromagnet, which is electrically connected to the controller and has magnetism when energized. A magnetic attraction member is provided on the recovered member 11, which is magnetically connected to the electromagnet.

[0068] The remote control center can control the electromagnet to be powered off to make the part to be recovered 11 break away from the restriction of the limiting part.

[0069] It should be noted that the structure of the limiter is not limited to an electromagnet, as long as the structure can achieve the effect that the limiter can achieve.

[0070] The to-be-recovered part 11 includes a parachute 111 and a data acquisition part 112. The data acquisition part 112 is used to collect and store required data information. The parachute 111 is connected to a remote control center for communication, and the remote control center is used to control the opening of the parachute 111.

[0071] When the high-altitude balloon 1 has been collecting data for a certain detection time at the predetermined floating height 8, the control limiter is opened, so that the recovery part 11 is free from the restriction of the high-altitude balloon 1 and falls downward. The detection time is affected by the wind speed and the release point 7, so that when the recovery part 11 is released and falls into the low-altitude area 14 again, the recovery part 11 is located above the ocean 12, so that the recovery part 11 can be affected by the sea breeze 4.

[0072] After the recoverable component 11 is free from the restriction of the high-altitude balloon 1, the parachute 111 opens to slow down the descent speed of the data acquisition component 112. The data acquisition component 112 will continue to descend in the direction away from the land 10 under the action of the high-altitude wind 2 until it lands at the critical line between the high-altitude wind 2 and the sea breeze 4, wherein the vertical falling speed of the data acquisition component 112 is greater than or equal to 1.5 m / s, and the vertical falling speed of the data acquisition component 112 is less than or equal to 2.5 m / s.

[0073] When the recovery object 11 drops to a position 2 km from the sea level (i.e., it drops to the critical position of the high-altitude wind 2 and the sea breeze 4), the recovery object 11 has fallen above the ocean 12. The recovery object 11 is affected by the sea breeze 4, and the recovery object 11 changes from moving away from the land 10 to moving closer to the land 10.

[0074] At this time, the horizontal distance between the recoverable component 11 and the land is greater than or equal to 5 km, and the horizontal distance between the recoverable component 11 and the land is less than or equal to 6 km, and the wind speed of the sea breeze 4 is greater than or equal to 5 m / s, and the wind speed of the sea breeze 4 is less than or equal to 6 m / s, which is sufficient to ensure that the recoverable component 11 successfully floats to the land 10 under the slow descent of the parachute 111.

[0075] The landing position of the object to be recovered 11 can be determined by pre-calculating the wind field. The issuing personnel only need to wait in advance at the recovery position 9. Eventually, the object to be recovered 11 will float to the recovery position 9 and be recovered by the issuing personnel. This effectively reduces the recovery pressure and difficulty, and solves the problem of high recovery difficulty in the existing high-altitude balloon 1 load recovery method.

[0076] The successful landing of the recovery part 11 on land 10 requires the following points to be met to ensure that the recovery part 11 will not fall into the sea:

[0077] 1. When the recovery part 11 descends to the critical line between the high-altitude wind 2 and the sea breeze 4, that is, when the height of the recovery part 11 to the sea level is 2 km, the horizontal distance between the recovery part 11 and the shore is greater than or equal to 5 km and less than or equal to 6 km.

[0078] 2. The vertical falling speed of the recovered part 11 is 2 m / s.

[0079] 3. The wind speed of sea breeze 4 is greater than or equal to 5 m / s, and the wind speed of sea breeze 4 is less than or equal to 6 m / s.

[0080] Furthermore, in order to accurately locate the recovery position 9 of the item to be recovered 11, the issuing personnel can adjust the release position of the item to be recovered 11 by calculating the wind force of the land wind 3 and the high-altitude wind 2 on the day of release through preliminary wind field collection, so as to ensure that each time the item to be recovered 11 is recovered, it can fall into the determined recovery position 9, which is convenient for the issuing personnel to recover it.

[0081] The specific manifestations are:

[0082] When the wind speed of land breeze 3 is greater than or equal to 2 m / s, and the wind speed of land breeze 3 is less than or equal to 5 m / s, the wind speed at the predetermined floating height 8 is greater than or equal to 15 m / s, and the wind speed at the predetermined floating height 8 is less than or equal to 40 m / s:

[0083] When the land wind 3 has the minimum wind speed of 2 m / s and the high-altitude wind 2 at the predetermined floating height 8 has the minimum wind speed of 15 m / s, the distance from the release point 7 to the ocean 12 is set to 100 km. At this time, the release route of the recovered component 11 is the release route 5 with the lowest wind speed.

[0084] When the land wind 3 has a maximum wind speed of 5 m / s and the high-altitude wind 2 at the predetermined floating height 8 has a maximum wind speed of 40 m / s, the distance from the release point 7 to the ocean 12 is set to 200 km. At this time, the release route of the recovered component 11 is the release route 6 with the highest wind speed.

[0085] Furthermore, in order to ensure that the component 11 to be recovered can fall onto the land 10 and more accurately fall onto the launching point 7, the remote control center can adjust the release time of the component 11 to be recovered based on the wind speed information sent back by the wind speed sensor and the current position information of the high-altitude balloon 1 (the position information includes the height of the high-altitude balloon 1 and the horizontal distance from the high-altitude balloon 1 to the launching point 7), thereby improving the landing accuracy of the component 11 to be recovered.

[0086] It should be noted that data collection can be performed as soon as the recoverable component 11 is released from the release point 7 and continues until the recoverable component 11 falls back into the lowering point and is recovered.

[0087] In summary, the wind field information is collected in advance, the launch point 7 is determined and the high-altitude balloon 1 is released. After the release, the balloon height information is collected in real time, and the balloon height information is used as a basis to determine whether the predetermined floating height 8 is reached. At the same time, the high-altitude balloon 1 will collect data in the process of being blown to the ocean by the land breeze; when the high-altitude balloon 1 rises to the predetermined floating height 8, the to-be-recovered part 11 is released, the to-be-recovered part 11 is separated from the high-altitude balloon 1, and the to-be-recovered part 11 is blown to the land by the sea breeze 4, and finally falls into the recovery position 9. The issuing personnel can wait at the recovery position 9 to realize the land recovery, and the issuing personnel do not need to recover at sea, which effectively reduces the recovery pressure and the difficulty of recovery, and solves the problem of high recovery difficulty of the existing high-altitude balloon 1 load recovery method.

[0088] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0089] It should be noted that the present invention takes a method for recovering a high-altitude balloon on land based on sea and land breezes as an example to introduce the specific structure and working principle of the present invention, but the application of the present invention is not limited to a method for recovering a high-altitude balloon on land based on sea and land breezes, and can also be applied to the production and use of other similar workpieces.

[0090] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recovering a high-altitude balloon on land based on sea and land breezes, characterized in that: include: Collecting wind field information in advance, wherein the wind field information includes the wind time, direction, speed of land wind, wind time, direction and speed of sea wind; Determine the launch point and release the high-altitude balloon; After the balloon is released, the balloon altitude information is collected in real time, and the balloon altitude information is used as a basis to determine whether the predetermined floating altitude has been reached; When the high-altitude balloon rises to a predetermined floating height, the part to be recovered is released.

2. The high-altitude balloon land recovery method based on sea and land breeze according to claim 1 is characterized in that: The launching point is set on land, and the high-altitude balloon will pass through the low-altitude area and enter the high-altitude area when blowing from land to the ocean, and finally rise to a predetermined floating height.

3. The high-altitude balloon land recovery method based on sea and land breeze according to claim 2 is characterized in that: The distance from the release point to the ocean is greater than or equal to 100 kilometers; And the distance from the release point to the ocean is less than or equal to 200 kilometers.

4. The high-altitude balloon land recovery method based on sea and land breeze according to claim 3 is characterized in that: The wind speed of the land breeze is greater than or equal to 2 m / s; And the wind speed of the land breeze is less than or equal to 5 meters per second.

5. The high-altitude balloon land recovery method based on sea and land breeze according to claim 4 is characterized in that: The distance from the predetermined floating altitude to the ground is greater than or equal to 18 kilometers; And the distance from the predetermined floating altitude to the ground is less than or equal to 22 kilometers.

6. The method for recovering a high-altitude balloon on land based on sea and land breeze according to claim 5, characterized in that: When the to-be-recovered part lands in the low-altitude area, the distance between the to-be-recovered part and the sea level is greater than or equal to 2 kilometers.

7. The method for recovering a high-altitude balloon on land based on sea and land breeze according to claim 6, characterized in that: When the to-be-recovered part lands in the low-altitude area, the horizontal distance between the to-be-recovered part and the recovery position is greater than or equal to 5 kilometers; And the horizontal distance from the to-be-recovered part to the recovery location is less than or equal to 6 kilometers.

8. The method for recovering a high-altitude balloon on land based on sea and land breeze according to claim 7, characterized in that: The to-be-recovered parts include a parachute and a data collection part, and the data collection part is used to collect and store data information; When the to-be-recovered component is separated from the parachute, the parachute opens to slow down the descent speed of the data acquisition component.

9. The method for recovering a high-altitude balloon on land based on sea and land breeze according to claim 8, characterized in that: The vertical falling speed of the data acquisition component is greater than or equal to 1.5 m / s; And the vertical falling speed of the data acquisition component is less than or equal to 2.5 meters per second.

10. The method for recovering a high-altitude balloon on land based on sea and land breeze according to claim 8, characterized in that: The wind speed of the sea breeze is greater than or equal to 5 m / s; And the wind speed of the sea breeze is less than or equal to 6 meters per second.

Images