Zhongmei DENG1, Liwen DENG2*, Liang WANG1, Gaoyu ZHOU1, Bangqun LU

1. Zigui County Forestry Science and Technology Promotion Center, Zigui 443600, China; 2. China Academy of Urban Planning and Design, Beijing 100044, China; 3. Zigui County Forestry Bureau, Zigui 443600, China

Abstract Taking the opportunity of the third monitoring of rocky desertification in the karst area of China, Zigui County of Hubei Province applied Unmanned Aerial Vehicle (UAV) for the first time for monitoring. Through repeated trials and studies, it established technical requirements including the UAV monitoring technology for the rocky desertification, the feature point photographing, UAV video judgment of rocky desertification degree, UAV video correction misclassification subcompartment, and UAV video observation of rocky desertification control. It completed the third rocky desertification monitoring task of karst area in Zigui County.

Key words Karst area, Rocky desertification, Monitoring, Unmanned Aerial Vehicle (UAV), Application

1 Introduction

This technical specification is established to regularly grasp the information on rocky desertification status and dynamic changes in karst areas, formulate rocky desertification prevention policies and ecological protection and restoration plans for the whole country and all areas, accelerate the ecological restoration of rocky desertification land, improve the regional ecological environment, and promote the construction of ecological civilization, and provide basic data for regional sustainable development. Taking the opportunity of the third monitoring of rocky desertification in the karst area of China, Zigui County of Hubei Province applied Unmanned Aerial Vehicle (UAV) for the first time for monitoring. Through repeated trials and studies, it has established a technical system for the application of UAV to monitor rocky desertification in karst areas, and completed the task of the third monitoring rocky desertification in karst area of China. The results were inspected and accepted by Hubei Province Forestry Investigation Planning Institute, Central South Forest Inventory and Planning Institute of National Forestry and Grassland Administration. This technical specification is prepared in order to guide and regulate the application of UAV for monitoring of rocky desertification in karst area.

This technical specification is proposed and exclusively administrated by Zigui County Forestry Bureau.

This technical specification is drafted by Zigui County Forestry Science and Technology Promotion Center and China Academy of Urban Planning and Design.

Main drafters of this technical specification include Deng Zhongmei, Deng Liwen, Wang Liang, and Zhou Gaoyu.

2 Scope of application

This technical specification specifies technical requirements including the UAV monitoring technology for the rocky desertification, the feature point photographing, UAV video judgment of rocky desertification degree, UAV video correction misclassification subcompartment, and UAV video observation of rocky desertification control.

This technical specification is applicable to the application of UAV in the rocky desertification monitoring of karst areas.

3 Normative reference standards

Provisions in following documents constitute provisions of this technical specification through citation. For cited dated documents, neither their subsequent amendment (excluding the corrigenda) nor revised edition is applicable to this standard, nevertheless, all parties coming to an agreement on the basis of this technical specification are encouraged to consider whether to apply the latest edition of these documents or not. For cited documents without date indication, the latest edition will apply in this technical specification.

TechnicalSpecificationfortheThirdMonitoringTechnologyforRockydesertificationinKarstAreas(Revised in 2016), State Forestry Administration[1].

ImplementationRulesforRockyDesertificationMonitoringinKarstAreasofHubeiProvince(2016), Hubei Province Forestry Investigation Planning Institute[2].

4 Terms and definitions

The following terms and definitions are applied in this technical specification.

4.1 KarstKarst refers to the unique landscape formed by carbonate-based soluble rock (limestone, dolomite, gypsum, rock salt) in the rock mass due to the dissolution and mechanical damage of the surface runoff and groundwater flow or on the surface of the rock formation. The karst plateau of Yugoslavia is a typical area, hence got the name "Karst"[3]. In May 1966, at the China’s Second National Karst Conference, "Karst" was used as the general term in China.

4.2 Rocky desertificationRocky desertification refers to the evolution process of outstanding contradiction between man and land, vegetation destruction, soil erosion, land production capacity decline or loss, and the surface of the rock gradually exposed to the desert landscape due to improper social and economic activities of human beings in the fragile karst ecological environment. In terms of causes, the main cause of rocky desertification is human activities.

4.3 MonitoringMonitoring refers to the long-term monitoring of the same object in real time to grasp its changes.

4.4 Unmanned Aerial Vehicle (UAV)An unmanned aerial vehicle (UAV) (or uncrewed aerial vehicle, commonly known as a drone) is an unmanned aircraft operated by radio remote control equipment and self-contained program control devices. There is no cabin on board, but equipment such as autopilot and program control devices are installed. Ground personnel track, locate, remotely control, remotely measure and digitally transmit through the equipment.

4.5 Feature pointsA feature point is a point that reflects the type of feature or the geographical distribution of the region. On the map, feature points have accurate geographic locations and clear geographic attributes and meanings.

4.6 Taking picturesIt is necessary to take pictures, to obtain static data and records of a certain point.

4.7 Taking videosTaking videos refers to making records of videos using optical or electromagnetic methods, also refers to recorded pictures.

4.8 VideoVideo generally refers to a variety of techniques that capture, record, process, store, transmit, and reproduce a series of static images in the form of electrical signals. When continuous image changes exceed 24 frames per second. According to the principle of visual persistence, the human eye cannot distinguish a single static picture; it appears to be a smooth continuous visual effect, such continuous picture is called video.

4.9 LevelThe level is the state in which people or things develop.

5 Basic conditions of the UAV

5.1 Aircraft Product typeFour axis air craft. Product positioning: professional film and commercial aerial photography. Flight load: 1 380 g. Working ambient temperature: -10-40℃. Satellite positioning module: GPS/GLONASS dual mode. GPS hovering accuracy: vertical: +/-0.1 m (within the ultrasonic working range), +/-0.5 m; horizontal: +/-0.3 m (within the visual sensor operating range), +/1.5 m. Lifting speed: maximum ascent speed: 6 m/s (sport mode), maximum descent speed: 4 m/s (sport mode). Flight speed: 20 m/s (sport mode). Flight altitude: ±500 m. Flight time: about 28 min. Wheel base: more than 350 mm. Propeller: 9450S quick release propeller.

5.2 Remote controllerOperating frequency: 2.400-2.483 GHz. FCC (flight control computer) control distance: 5 000 m; (no interference, no occlusion) CE: 3 500 mm.

5.3 PlatformPhantom 4 integrated platform camera. Controllable range of rotation: -90°±30°. Control speed: adjustable.

5.4 CameraLens: FOV 94°20 mm (35 mm format equivalent) f/2.8 infinity focus. Sensor: 1/2.3 inch CMOS, effective pixels 12.4 million (total pixels 12.76 million). ISO range: 100-3 200 (video); 100-1 600 (picture). Shutter speed: 8-1/8 000 s. Picture resolution: 4 000×3 000. Video resolution: UHD: 4 096×2 160 (4K) 24/25 p; 3 840×2 160 (4K) 24/25/ 30 p; 2 704×1 520 (2.7 K) 24/25/30 p. FHD: 1 920×1 080 24/25/30/48/50/60/120. HD: 1 280×720 24/25/30/48/50/60 p. Shooting mode: single shot. BURST: 3/5/7 shots. Auto exposure bracketing (AEB): 3/5 shots at 0.7 EV. Timed shooting. HDR. File format: image format: JPEG, DNG (RAW). Video format: MP4/MOV (MPEG-4 AVC/H.264). Memory card type: standard 16 GB Micro SD card, maximum support 64 GB capacity, transmission speed of Class 10 and above or UHS-1 rated Micro SD card.

5.5 Power performanceCharger: Phantom 4 intelligent battery charger. Battery: Phantom 4 intelligent flying battery.

5.6 Other parametersInterface: the remote control has a USB interface; the body is arranged with a Micro USB interface. Compatible platform: iOS version v2.7.1, iOS 8.0 or higher required. Compatible with iPhone 5s, iPhone 6, iPhone 6 Plus, iPad Air, iPad Air Wi-Fi+Cellular, iPad mini 2, iPad mini 2 Wi-Fi+Cellular, iPad Air 2, iPad Air 2 Wi-Fi+Cellular, iPad mini 3 and iPad mini 3 Wi-Fi+C.

6 Monitoring contents

The feature points are photographed, use the UAV video to determine the degree of rocky desertification, and the UAV video to correct the misclassified subcompartment, using UAV video, to observe the control of rocky desertification.

7 Preparation before monitoring

7.1 Information collectorBased on the previous rocky desertification monitoring data and the latest remote sensing images (RS), the GIS is used to carry out subcompartment zoning and interpretation, and the subcompartment and interpretation of the zoning is imported into the information collector provided with Global Positioning System (GPS), to compare in situ with the UAV.

7.2 GPS correctionTaking the GPS data of the information collector as the basis, the UAV is superimposed on the information collector, the center point is aligned, the GPS data of the UAV is read, and the positive and negative values (±Y, ±X) are calculated.

7.3 Design of feature pointsAccording to different conditions and degree requirements, the feature points are designed to subcompartment.

7.4 Preparation of field survey cardPreparation of field surrey carrd was shown in Fig.1.

Fig. 1 UAV camera monitoring record of rocky desertification

7.5 UAV flight designAccording to the requirements of feature points, check the flight distance of the subcompartment and the UAV, determine the takeoff point of the UAV. The principle of determining the take-off point is: the terrain is wide, the visibility is large, and it is able to observe multiple feature points and verify subcompartment as much as possible.

8 UAV flight conditions

8.1 General conditionsThe operating area is sunny or cloudy without fog, visibility is greater than 200 m, wind power is less than level 4, and flying is possible.

8.2 Optimum conditionsThe optimum conditions are as follows: operating area is sunny without fog, visibility is greater than 500 m, wind power is less than level 2.

8.3 Unfavorable conditionsThe operating area is or cloudy or rainy, or there is fog, visibility is smaller than 100 m, wind power is greater than level 4, and flying is not allowed.

9 Monitoring methods

9.1 Taking pictures of feature pointsStart the information collector at the takeoff point, and find the feature point subcompartment. The UAV flies to the space above the feature point subcompartment, the information collector compares with the UAV videos. The UAV rises to the level where it can observe the full scene of the subcompartment and vertically hovers to take pictures. The UAV descends to the level of 50 mm above the feature point that can represent the feature of subcompartment and vertically takes pictures. Make records in the field survey card.

9.2 Using UAV video to judge the rocky desertification degreeStart the information collector at the takeoff point, and find the subcompartment to be checked. The UAV flies to the space above the subcompartment, the information collector compares with the UAV videos. The UAV rises to and hovers at the level where it can observe the full scene of the subcompartment. Through the UAV video, observe the vegetation coverage proportion, and make records in the field survey card.

9.3 Using UAV video to correct the misclassified subcompartmentStart the information collector at the takeoff point, and find the subcompartment to be checked. The UAV flies to the space above the subcompartment, the information collector compares with the UAV videos. The UAV rises to and hovers at the level where it can observe the full scene of the subcompartment. Through comparison between the UAV video and information collector, correct the misclassified subcompartment in the information collector. Make records in the field survey card.

9.4 Using UAV video to observe the control of rocky desertificationStart the information collector at the takeoff point, and find the control area to be checked. The UAV flies to the space above the control area, the information collector compares with the UAV videos. The UAV rises to and hovers at the level where it can observe the full scene of the control area. Through comparison between the UAV video and information collector, plot the control subcompartment in the information collector. Make records in the field survey card.

10 Internal data processing

10.1 Information collectionImport the contents of the information collector into the software of the computer equipped with "rocky desertification monitoring software". Import pictures taken by the UAV to the computer desktop.

10.2 Correcting GPS valueAccording to the corrected value of GPS, correct the GPS value for the pictures taken by the UAV.

10.3 Importing picturesImport the pictures taken by the UAV with the corrected GPS value (Fig.2) into the "rock desertification monitoring software".

Fig.2 Third monitoring of rocky desertification UAV field survey feature point picture in Zigui County (Huangkouping Village, Guojiaba Town)

10.4 Correcting attributes and factorsIn the "rock desertification monitoring software", conduct correction according to the contents of field survey card.

11 Monitoring results

In the third monitoring of rocky desertification in the karst area of China, Zigui County used the UAV to survey the rocky desertification and surveyed a total of 5 406 subcompartments and reviewed 196 feature points. According to the monitoring results, Zigui County has karst area of 124 215.4 ha, a rocky desertification area of 33 902.2 ha, accounting for 27.29% of the total area of the karst area, and a potential rocky desertification area of 62 177.2 ha, accounting for 50.06% of the total area of the karst area, and non rocky desertification area is 28 136 ha, accounting for 22.65% of the total area of the karst area[4].

In the rocky desertification area, the area of mild rocky desertification is 13 715.1 ha; the area of moderate rocky desertification is 15 756.3 ha; the area of severe rocky desertification is 4 216.8 ha; and the area of extremely severe rocky desertification is 214 ha.

12 Existing problems

12.1 Not available in mountain streams and canyonsUAV take-off conditions have high requirements for satellite signals. In places with weak satellite signals such as mountain streams and canyons of mountainous areas, takeoff requirements could not be satisfied, so UAV is not available.

12.2 Restriction by weather conditionsThe operation of UAV is restricted by weather conditions. The UAV can not be used in visibility less than 100 m, the wind power greater than level 4, and can not be used in rainy days.

12.3 Difficult to determine the positionDJI Phantom 4 Pro drone could not display the position in real time, and it is difficult to determine the position according to the video pictures of the drone.