Drones, Remote Sensing and GIS: Low Cost Applications for Organic Farming and Land Management Decisions

Introduction

Aerial imagery and mapping applications for farm planning and management can be accomplished with a cost effective approach. Essentially, acquiring aerial imagery will provide valuable information to assist with decisions of farm management, planning and design with the ability to conduct a low cost survey for acquiring, processing, and manipulating RGB aerial imagery data for high quality map products and measurement estimates.  Small unmanned aerial systems (sUAS) with instrumentation payloads can be utilized rapidly for small and large scale farm applications. Today, there are many options to choose from but can be overwhelming with pros and cons which could be best suited to another post.

The use of sUAS or drones for acquiring aerial imagery is pretty straight forward, but must be performed in accordance with FAA regulations, have a proper flight or mission plan to acquire the data necessary for post processing applications and support high quality map products. Structure from motion (SfM) applications are accomplished with photogrammetric algorithm software with internal algorithms that correct mis-alignments caused by any lens radial and tangential distortion effects for high resolution dense point cloud georeferenced digital elevation models (DEMs) and orthomosaic maps. In order to achieve precise measurements at high resolution, the imagery is georeferenced with well distributed ground control points (GCP’s) and/or tie points with DGPS survey. The RGB sensor data is processed with GIS software and data manipulated tools to produce high valued maps and measurements. The high resolution topographic models and orthorectified photomosaics generated in GIS are used to produce professional map products. Other high value products includes: 1) crop health assessments, utilizing the triangular greenness index (TGI), correlates well with the conditions present and shows promise in helping evaluate plant growing conditions; 2) compost and mulch volume measurement estimates were completed and give rapid volumetric data to interested parties. In addition to survey mapping, a farm asset allocation evaluation is presented herein. 

Low cost “off the shelf” sUAS’s combined with durable action cameras and sufficient mission planning, data collection and processing have the capability to effectively and efficiently outperform costlier platforms and multi-spectral instrumentation packages. The cost benefit of the sUAS survey has value in assisting with important farm planning and land management solutions for profitable sustainable organic applications.

Objectives

The primary focus of this study is to acquire high resolution imagery to generate orthomosaic photos and DSM’s for map production and 3-D measurements. We will use georeferencing methods and SfM for post-processing applications and final products. The processed data sets are used to assess the hydrology, map and measure crop-bed dimensions, and material volume (e.g. mulch and compost piles). The final map publications and measurements will assist with the analysis and decision making process for sustainable farm planning, design, construction, and resource management. In order to achieve high ground resolution, a ground sample distance of minimum 5 cm (GSD) should be obtained. Figure 2 presents the general project workflow.

1. Orthomosaic
   • Georeferenced (Orthorectified) professional map.
   • Identify land zones/crops and assets
     1. Access
     2. Structures
     3. Greenhouses
     4. Farmland (existing crop beds/rows, virgin soil, cover crop)
2. Farmland Assets: % of existing and potential ground
   • Farming limits/access
   • Current use vs. virgin ground/covercrops
   • Farmland expansion potential/suitability
3. Digital Elevation Model (DEM)
   • High resolution topographic map
     • Hydraulic (surface water) conditions and trends
     • Sources of erosion, ponding water, and/or
     • Identify more sustainable gravity-driven water diversion systems
4. Compost / Mulch Piles Measurement
   • Volume estimate
   • Plan and design of soil amendment area calculations
5. Crop Health Evaluation
   • Current plant stress conditions
   • Spatial-Temporal plant stress patterns/trends
   • Triangulated Greenness Index (TGI)
     • Chlorophyll spectral features

Crop Health Assessment (TGI)

While utilizing GIS, a choropleth was created to ascertain the health, or “greenness”, of flora. This is accomplished by separating the red, green and blue bands from the combined RGB data created in data processing software from the photographs. Once separation was complete, raster math was utilized to combine the segregated bands into a mosaic that indicates the leaf nitrogen content. Leaf nitrogen and chlorophyll content are related and indicate overall plant health (USDA, 2013). Leaf area index (LAI) of surrounding plants and soil type need to be taken into account as their presence can skew the data. However, closed canopy is the best situation for true TGI reading of the target species as only representative species are indexed. The TGI is defined as: −0.5[(670 − 480)(R670 − R550) − (670 − 550)(R670 − R480)] (USDA 2013).

In general, Triangulated Greenness Index (TGI) is representative of crop health. LAI intrusion from lower story flora and soil characteristics were notable, causing some skewing of the data, however, patterns could be distinguished readily. The TGI performed, Figure 2, shows rows of crops (cabbage) indicating an overarching pattern of superior greenness, suggesting less stress and preferable growing conditions exist within the confines of a homogenous crop.

Conclusion

The RGB imagery provided data required for conducting a general farm survey using sUAS at relatively low cost in a limited amount of time. High quality mapping and measurements to scale were performed using products generated from structure from motion (SfM) photogrammetry software, and further processed and manipulated with GISsoftware.  This project is a pilot study on the capability for sUAs and low cost equipment to perform high quality surveys for professional map products and additional analysis for a property including assessments of crop health, hydrology, and land value and conditions.

If you would like more information about drone imagery mapping services and products, contact HGX or write a comment to this post below.