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UAV Protocols

Authors: Rick Ward

Abstract

Multispectral data collected during seasons 1-5 at Maricopa using small unmanned aircraft systems, i.e. UAVs. Workflow includes image capture with cameras on UAV platforms, generation of georeferenced orthomosic reflectance and index (e.g. NDVI) geotiffs, extraction of plot level statistics within qgis with the aid of polygon shape files in which plot attributes are stored. Downstream users can access the radiometric and index data from the reflectance map geotiffs directly, or from the plot level data uploads.

Materials

Platforms

  • SenseFly eBee fixed-wing drone

  • Hexacopter

Cameras

UAV data are collected using one of three cameras:

Cameras are carried singly or in tandem on the SenseFly eBee fixed-wing drone (Sequoia and thermoMap, individually only), or a hexacopter (RedEdge or Sequoia, individually or in tandem).

Procedure

Flight

Standard flight altitude is 44m with 75% image overlap (both sequentially and laterally), and missions are programmed and managed by either Mission Planner or senseFly eMotion.

Calibration

No radiometric calibration was conducted as of Nov 5, 2016.

Analysis

Pix4D software was used to generate gray-scale orthomosaic geotiff files containing NDVI data after georegistration to the WGS84/UTM 12 N coordinate reference system using three to five 2D geo-located ground control points. These are manually matched to 5-40 images each. Ground control points for the Lemnatec Field Scanner are on the concrete pylons and were geolocated using an RTK base station maintained by the USDA-ARS at Maricopa (see section on geospatial information).

QGIS software was used to confirm geospatial alignment of NDVI geotiffs with shape files containing geolocated positions of the rail foundations. A shape file containing polygons aligning with the middle two rows of each of the 350 experimental units (for sorghum crop Aug-Nov 2016) was kindly generated by Dr. A French of USDA-ARS. Zonal Statistics in QGIS was used to calculate NDVI means for each plot polygon.

References

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