Practical application of unmanned aerial vehicles for monitoring and inventory of agricultural lands
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UDC 528. 46:528. 7(203)-047. 36
PRACTICAL APPLICATION OF UNMANNED AERIAL VEHICLES FOR MONITORING AND INVENTORY OF AGRICULTURAL LANDS
Varvarina E.A., Post-graduate student State University of Land Management, Moscow, Russia E-mail: varvarinakatya@rambler. ru
The article under review considers the experience of practical application of methods of small aviation for the solution of local problems in agriculture, particularly, monitoring and inventory of lands. The basic idea is to create cartographic materials on the base of orthophotomaps in scale 1: 5000, made with the use of unmanned aerial vehicles. Special attention is paid to the evaluation of accuracy of the phototrigonometrical network construction, the digital relief models construction, and as a result to the evaluation of the accuracy of the orthophotomap construction. The examples of the applied purpose of the orthophotomaps created are given.
Photogrammetry- Remote sensing- Construction- Large-scale ortophotoplans- Unmanned aerial vehicles- Aerial photography- Agriculture- Remote monitoring methods.
Today Russia'-s agricultural enterprises face the problem of land administration system modernization, that'-s why it is necessary to know the real size of cultivated areas of an agricultural enterprise for the efficient management.
Often, enterprises operate figures on the basis of the inventory data of the 1970s, that negatively influences both the accuracy of agricultural measures and the economic efficiency of agricultural production. Thus, the modern agricultural enterprises face the challenge of precision farming. The precision farming is the highest form of adaptive-landscape farming, based on the high agro-technologies with a high degree of adaptability. The base of the scientific concept of precision farming is the existence of inhomogeneity within one field.
A field is a group of land plots used for agriculture and having single crop rotation. The modern technologies such as global positioning systems, special sensors, remote sensing data (of large and small aircraft), as well as special programs for agro-management are used for monitoring, evaluation and detection of these inhomogeneities.
The data collected are used for planning of sowing works, calculation of fertilizers norms, means of plant protection, and yields using the field maps (Field maps are shown in Figures 1−2).
Figure 1 — Field map Figure 2 — Field map
The field map as the name implies is a digital land model, containing information about the contours of the agricultural plots, marked in accordance with the land management plan of the agricultural enterprise or internal rules of the identification for fields of the specific agricultural enterprises- the graphic image of the field maps has the vector description of the
external and internal contours of agricultural land and explanatory texts describing the fields of crop rotation and their parts.
The main problem that should be solved for the field mapping is the formation of the arable lands with homogenious soil composition. In practice, this task is difficult to be solved, because we have to work on the plots of small size, that leads to difficulties in field cultivation. The majority of agricultural enterprises try to generalize working areas, as it allows to use the wide-cut agricultural equipment most efficiently, thereby reducing the cost of operation of heavy equipment and its effect on the soil.
For the best economic efficiency, agricultural enterprise can fertilize only those parts of the fields that need it. For this purpose the technology of differential fertilizer application is used through the global positioning systems. The remote sensing data help to solve these and many other tasks of agricultural enterprises.
Despite the advent of air laser scanning, satellite imagery and other remote sensing methods, a large-scale mapping of relatively small plots of about 30 square kilometers is still problematic.
The reasons are that it is difficult to get accurate data through satellite surveys, ground surveys on the plots of more than 1 square kilometer don'-t meet the requirements of efficiency and require a significant money investment, and the use of the air laser scanning method to photograph plots of 10 square kilometers is economically inexpedient.
At the same time practice shows that often aerial photos and maps-materials of small plots of 30 square kilometers in scale 1: 5000 and larger are demanded for such purposes as: landscape design- development of architectural and environmental solutions- designing of local line networks (power lines, local roads, gas and oil pipelines) — evaluation of profitability, etc.
The solution of such problems is significantly simplified through a large-scale aerial photography . In this regard, unmanned aerial vehicles gained a wide popularity due to the possibility of getting specific technical information of the surroundings, where it is difficult to place an operator. The development of computational techniques and digital signal processing technology significantly has allowed to improve the quality, speed and volumes of images processing, provide their transmission over large distances. However, digital technologies have their drawbacks that influence the effectiveness of their use in prospecting and monitoring. The optical systems in unmanned flying technique are used for: monitoring the area- obtaining detailed images of the area and objects located on it- discovering visible objects and invisible ones.
The technical systems are implemented in the form of optical devices, placed either directly to the aircraft and tightly connected with its frame or by means of gyro stabilized platforms, that ensure the rotation of the optical axes of devices in any direction with the set speed. As a rule, a tight connection of the optical axis of the device with the frame of the aircraft is used for aviation apparatus and optical devices of observing the front or other hemispheres of the aircraft. The term & quot-tight connection& quot- is relative. Almost all optical devices installed into the frame of the aircraft have the feature of some angular displacement to compensate the angular position of an aircraft relative to the earth surface and the angular aircraft fluctuations relative to the axes of the normal coordinate system .
Using unmanned aerial vehicles in the civil sector is currently waiting for the solution of some technical and organizational problems, which are essential for the sustainable use of unmanned aerial vehicles.
The main problems are connected with the use of airspace, getting a partial range to control the UAV and the transmission of information from board to earth and back and, finally, with the development of the civil service market, which is at the formation stage. The use of the unmanned aerial vehicles is of great importance nowadays.
First of all we should mention the control functions of unmanned aerial vehicles. Using unmanned systems many points can be controlled such as a technical condition of objects, and secure functioning, even when the objects controlled may be at a great distance. It is necessary to make potential users of unmanned aerial vehicles initiate the rules of using unmanned aerial vehicles in the civil sector. The main issue is getting the status of the aircraft for unmanned aerial vehicles. The unmanned aerial vehicles are not recognized as aircraft and are not subject to registration as an aircraft. It is impossible to get a license for
using the airspace. An apparatus capable to fly 4 km high at the speed of 250 km/hour, weighing about 100 kg, can get in the air without permission to use airspace, because according to the classification it is a radio-controlled model. Within the current legislation there is a type of aviation, where the unmanned aerial vehicles are considered to be an experimental aviation on legal ground. 
In connection with the fact that this aircraft is not official, hence, there are no legal documents and regulations governing the survey using unmanned aerial vehicles.
This paper will detail all complex of works on creation of orthophotomap in scale 1: 5000 for vast territories, which includes the following stages: the development of a technical project for the aerial survey works- drawing up a project of a field survey control- creation of a field survey control by means of double-frequency geodesic satellite equipment- conducting aerial surveys- photogrammetric processing of aerial survey data.
The works were carried out on the territory of the Moscow region in the Dmitrovsky municipal area. All the works are done in the UTM projection 37N on the datum WGS-84.
EQUIPMENT AND TOOLS
The aerial survey works were carried out using several aircrafts: unmanned aircraft system «Irkut-10» and aerial survey complex on the base of UAV «0rlan-10». The UAV «Irkut-10» is intended for television observation on a flight route for the subjacent surface and the objects on it in real time operation mode in the conditions of natural light day and night, as well as for the aerial survey in the day conditions.
& quot-Irkut-10"- can be used on plain, mountainous and cross country from any site providing a direct radio visibility between the UAV and ground control station. The set of equipment to be used for aerial survey consists of a gyro stabilized platform for fixing an aerial camera on it. A digital camera SIGMA-DP2S was used for aerial survey. The on-board GPS equipment and an aerial camera provide the coordinates of the projections centers of the airphotos during the aerial survey. The set of equipment to be used for aerial survey includes digital one-objective lens reflecting camera CANON EOS 5D Mark II, Integrated autopilot fixed-frequency receiver GPS/GLONASS and GPS/GLONASS receiver Javad TRE-G3T, L1/L2.
Devices for horizontal and vertical tie-in. The works on the horizontal and vertical tie-in were done using double- frequency geodesic satellite equipment GB-500 of TopconPositioningSystem company with post-processing of satellite observations from the discovered and surveyed points of the state geodesic network (hereinafter SGN). In the future, to optimize and accelerate the works the Satellite system for surveying the land (the project «Moscow») was used, OAO «Goszemcadastrysiomka» — VISHAGI. A rented-Satellite equipment — LEICA SR530, worked in RTK (Real Time Kinematic) on differential corrections transmitted by Satellite system of land surveying in the real-time mode.
CREATING FIELD SURVEY CONTROL
Defining the points of the field survey was done to provide the aerial surveys with the starting base for the creation of orthophotomap on the territory of the Dmitrovskiy district of the Moscow region. The works on the field survey points were done by the two technologies.
The first technology involves the use of double-frequency double-system geodesic satellite equipment GB-500 of TopconPositioningSystem company with post-processing of satellite observations from the discovered and surveyed SGN points (this equipment is used if there is no connection for work in the RTK mode in the working area). The second technology of work involves the use of a Satellite system for surveying the land (the project «Moscow»), OAO «Goszemcadastrysiomka» -VISHAGI. The satellite equipment will work in the real-time mode on differential corrections transmitted by the Satellite system of land surveying in the real-time mode.
The works on field survey included the following stages:
1. Making a field survey photo and layout of PVP points.
2. Recognition of the PVP points and observations with the use of geodesic satellite equipment.
During the project creation of the field survey, the preliminary approximate coordinates of the PVP points planned are determined. When working in the field using GPS receiver Garmin the approximate location of the PVP chosen was determined by the approximate coordinates- a surely visible contour was determined afield. It is shown in Figure 3−4:
Figure 3 — Field map Figure 4 — Field map
A geodesic satellite equipment receiver was fixed on the counter chosen, as shown in Figure 5:
The realization of the differential method is schematically shown in Figure 6. A satellite receiver is located on the point with the already known coordinates (RTK base station operates permanently), another receiver is put on a point defined. The record of satellite measurements is done synchronously on the both points.
Figure 6 — Differential method
The coordinates of the point defined are got relative to a known point.
3. Preliminary processing of the observations done.
Preprocessing consists in the following stages. The field observations are got from the geodesic receivers of the satellite equipment. The contours of the PVP points observed are got. The following data are written down: name of the PVP point, time of the observation, the height of the antenna standing.
4. The adjustment of the PVP points.
At the adjustment stage the field observations are loaded down in the processing program, the names of the points are put into the program according to the PVP project, the height of the device of standing is stated.
The adjustment, PVP points coordinates determination relative to GNS points are done- the base station continuously transmits corrections in the RTK mode and the receiver immediately translates onto a screen, recorded into the memory the end adjusted coordinates of the PVP point.
The project of the field survey was developed in the program GIS & quot-Map 2011& quot-. All the works were done according to the instructions on the development of the survey control and photographing situation and relief with the use of global navigation satellite systems GLONASS and GPS, GKINP (ONTA)-02−262−02.
The requirements for the PVP determination to create orthophotomap in scale 1: 5000 according to the instructions for photogrammetric work to create topographic maps and plans «GKINP (GNTA)-02−036−02» presented to the digital images and large-scale row, Table 1.
Table 1 — Accuracy of the survey geodesic network points
1: 5000 1: 2000 1: 1000 1: 500 1: 200 1: 100
Accuracy of the survey geodesic network points used for photogrammetric bridging mx, y (m) 0,50 0,20 0,10 0,05 0,02 0,01
The points of the state geodesic network, geodesic networks bridging and points of survey geodesic networks defined for field preparation of images were the field survey control for creating topographic maps and plans. The points of the survey geodesic networks used for photogrammetric bridging, must have an average error in the plan, that does not exceed 0.1 mm in scale of the map (or plan) made and 0.1 of the vertical interval assumed of the height (relative to the nearest points of the state geodesic network and geodesic networks bridging). The scheme of satellite-based definitions with the use of the doublefrequency geodesic satellite equipment GB-500 of Topcon Positioning System company is shown in Figure 7:
Figure 7 — Satellite-based definitions with the use of the double-frequency geodesic satellite
In the centre of the working area the central point (or PVP project point maximally close to the center of the plot) was chosen. The determination of the central point coordinates by the method of «control network development by constructing a network» from two SGN points, simultaneously at least three units were used. The definition of the other PVP points at the plot where the works were done from the central point by the method of «survey control development, the definition of hanging points». The time of the central point determination is not less than an hour from the SGN points.
When using the satellite equipment LEICA SR530 working in RTK mode on differential corrections transmitted by the Satellite system of land surveying in the real-time mode, the definitions were done simultaneously from the 3 basic differential stations.
The maximum offset of the PVP points from the central point judging by the accuracy of the double-frequency double-system geodesic satellite equipment for GB-500: in plan 5 mm + 1.5 mm/km- statics (h) 10 mm + 1.5 mm/km. For LEICA SR530: in plan 5 mm + 1 ppm- height 10 mm + 2 mm/km.
The satellite measurements processing using GB-500 was done in the Pinnaclever 1.0 program. The scheme of the base stations location of a Satellite system of the land surveying (the project «Moscow»), OAO «Goszemcadastrysiomka» — VISHAGI is shown in Figure 8:
Figure 8 — Scheme of the base stations location
According to the results of satellite definitions of the PVP points the maximum error did not exceed 0. 20 per meter. The determination of coordinates and height was done in the geodesic coordinate system WGS-84 in the UTM 37N projection. As a result of works the following materials were formed: field survey control project made in GIS & quot-Map 2011& quot-- the certain PVP points coordinates catalogue- contours of the points with the descriptions. Accuracy of definition of coordinates and height of the control points entirely met the requirements of the Assignment Specification.
Aerial works were done in strict accordance with the requirements set: «the main provisions of the aerial survey for creating and updating topographical maps and plans GKINP-09−32−80», Moscow, «Nedra», 1982- «Surveying Flights Manual», Moscow «Air transport», 1983- «Aerial Mapping Works Manual», Moscow, RIO, 1976 and Assignment Specifications.
The aerial works for all objects were based on control survey points. While doing aerial survey of the objects the routes were oriented parallel to the edges of the surveying plot. The territory of each object during the aerial surveys was covered by double images with a buffer zone from boundaries of the plot not less than 50m.
Figure 9 — Field map Figure 10- Field map
The overlaps of images when using unmanned aircraft system & quot-Irkut-10"-, equaled: forward lap 60% - 65%- lateral lap 30% - 33%. The overlaps of images when using complex on the basis of UAV «0rlan-10″ equaled: forward lap 80%- lateral lap 60%. The aerial surveys were done in clear air and the height of the Sun above the horizon at least 20 degrees. The weather conditions were favorable for the aerial surveys. The examples of images are shown in Figures 9−10.
The photogrammetric works were done to create orthophotomaps in scale 1: 5000. The creation of the digital relief model and orthophotomap was done using a photogrammetric system PHOTOMOD 5. 23.
A photogrammetric processing of the aerial survey data is based on the following stages: creation of the project- definition of the internal orientation elements- downloading of the external orientation elements, formation of the block scheme- network measurement, searching the change points- network adjustment- digital relief model creation- orthophotomap creation.
The relative orientation was done by measuring the change points on the images. When processing PVO the method of change points adjustment was adopted. As a result of photogrammetric processing the following materials were obtained: catalog of external orientation elements- digital relief model in the form of irregular Delone'-s grid (TIN) — digital relief model in the form of a regular block (altitude matrix) — orthophotomap, with accuracy corresponding to scale 1: 5000. The example of an orthophotomap is shown in Figure 11.
Figure 11 — Field map
The average errors of the clear contours and objects in the photomap which are on the earth surface relative to the nearest points of the planned survey control do not exceed 0,5 mm in the photomap scale.
The average values of differences in plan points coordinates field survey control and photogrammetric network measured on the transformed image and available in a catalogue do not exceed 0,7 mm in plan scale.
The works were done in accordance with the Assignment Specifications and „Instructions for photogrammetric processing for creating digital topographic maps and plans“ GKINP — 02−036−02.
CONTROL AND ACCEPTANCE OF FIELD AND CAMERAL WORKS
The control and acceptance of work at all stages of production were organized and carried out on the basis of the „Instructions on the procedure for control and acceptance of geodesic, topographic and cartographic works“, GKINP (GNTA) 17−499, Moscow, CNIIGAK, 1999.
The monitoring was carried out in the following parameters: control of correspondence of processes and results of the works done and their registration to the requirements of technical projects and normative acts- identification of the completion degree- prevention of the mistakes in work- control of the devices and additional equipment state.
Control and acceptance of field surveying and aerial survey was carried out during all the surveying period and covers all the technological processes. Monitoring of the field works was combined with their acceptance. The field control was done with geodesic satellite equipment choosing several PVP points by random and re-defining their coordinates. The measurement was done relative to SGN point or control point network, from which the PVP points were determined. Requirements to the tolerance-discrepancy of the coordinates of PVP points defined in different period of time, differ not more than 5 cm. According to the monitoring the received materials of aerial photography and the coordinates of the PVP points were transferred for further office processing.
In the course of cameral works the following methods of control were used: input control of incoming data (was done to establish the quality of the photographic material and its conformity with requirements of technical documentation, modern standards, and also the estimation of opportunities of using this material when doing laboratory works) — visual control of the parameters, when estimating photographic products.
Control of photogrammetric production was based on the following parameters: at the stage of the relative orientation there were determined images errors, arrangement tie points errors. The results are given in Table 2.
Table 2 — Parameters for control of photogrammetric production
Ex Ey Ez Exy (metre)
0. 177 0. 116 0. 739 0. 212
At the stage of the exterior orientation a quality control of the ground coordinates determination was done. The results are given in Table 3.
Table 3 — Quality control of the ground coordinates determination
N Xcp-Xr Ycp-Yr Zcp-Zr Exy (metre)
552 -0. 030 -0. 017 0. 008 0. 034
553 -0. 083 0. 002 0. 134 — 0. 083
554 -0. 258 -0. 850 -0. 120 0. 888
555 -0. 710 -0. 402 -0. 169 0. 816
Middle module 0. 270 0. 318 0. 108 0. 455
CKO 0. 380 0. 470 0. 123 0. 605
max 0. 710 0. 850 0. 169 0. 888
At the stage of images orthophototransforming a final product quality control was done through the control points, also there were identified the errors in the digital relief model. The results are given in Table 4.
Table 4 — Control points for final product quality control
Ex Ey Ez Exy (metre)
0. 221 0. 157 0. 566 0. 317
Orthophotomap accuracy control is given in Table 5.
Table 5 — Orthophotomap accuracy control
Number of the images in the mosaic: 130
Declinations Ex Ey Exy
Mean square: 0. 412 0. 560 0. 718
Middle module: 0. 312 0. 407 0. 566
max & quot-+"- 0,755 0,881 0,911
max & quot--"- 0,463 0,612 —
For good farming it is necessary to know the area, its relief, that'-s why the horizontals were constructed on the base of the digital relief model data, that allow to understand the general view of the area. The topographic scheme is presented in Figure 12.
Figure 12 — Field map
Also according to the digital relief model a triangulation surface was constructed which describes the area. (Figures 13−14):
Figure 13 Figure 14
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