Eyes in the sky
By Dale Steele P.Ag. Precision Agronomist
As farm acreage grows, it is virtually impossible to know every part of the field and to scout every acre. Remote sensing is simply defined as collecting field information remotely from a remote platform. Satellites, planes, UAVs/drones or equipment mounted platforms can provide a bird’s-eye view of the field to collect information and see field variability and patterns that you can’t readily detect as you walk across a field.
Watching kids grow up, you don’t notice the subtle changes each week, but looking back over a few years of family pictures enables you to see dramatic changes. Pictures are also useful in agriculture to capture the moment and review the history.
Your farm actually has a tremendous imagery archive, although you probably have never seen it. Airplanes and satellites have been collecting imagery of your fields for years. In Alberta, air photos are available back to 1949 for most farmland. Landsat satellites started collecting multi-spectral imagery in 1972 and Landsat 8 continues building that 44-year archive. Google Earth was available in 2005 with a collection of true colour images of the Earth. The RapidEye satellite network was launched in 2009 with field detail and re-visit dates more suited to agriculture. Lethbridge based Ventus Geospatial was established as one of the first UAV/drone service providers in 2012, well ahead of the emerging U.S. market.
Technology advances have improved the camera and sensors to deliver amazing field detail every week of the growing season. Satellites and UAV/drone images can show excellent field detail. As a chemical rep, I took a lot of field pictures before the new smartphone apps could locate, store and share those important areas of interest. Now you can see layers of information on your tablet as you walk across the field to assess field areas with GPS precision.
Remote sensing is a broad discipline and I encourage you to build your background knowledge using Internet searches. For agriculture, you want to know some basic information when viewing imagery of your fields. Vegetation can be measured with different wavelengths of the electromagnetic spectrum that our eyes can’t see. Near-infrared (NIR) and normalized difference vegetation index (NDVI) values are accepted measurements of vegetation that contain much more information than true colour pictures. Ask: What is the resolution or pixel size? What platform collected the image using what sensors? What is the image date and relative crop stage? What type of image processing was used?
Orthorectification ensures the image scale is correct for the field, just as most fishermen know that the tilt and background references can make their fish look much larger in pictures.
I find most farmers are skeptical about remote sensing, field variability and vegetation differences until they see their own fields with NIR vegetation detail from the RapidEye satellites or UAV/drones. Each image platform has pros and cons pertaining to the resolution and cost of collecting this field information. High resolution UAV/drone imagery can become terabytes of data that require good software to stitch together multiple images and GPS coordinates to quantify the data and the clouds that limit satellite image capture. Even now, lack of farmer access to multi-spectral crop imagery remains a barrier, but as precision agriculture acres have grown, imagery costs have been reduced dramatically. RapidEye satellite imagery access can start at $0.50/acre and UAV/drone imagery is approaching $3 to $4 per acre. Satshot provides access to the imagery from numerous satellite networks along with information and imagery processing options.
A picture is worth a thousand words. One picture can identify issues in the growing season, but the power of imagery is it enables change detection on a massive scale. If nature and crop growth were predictable, we could just seed, spray and harvest on the same calendar dates each year. But farming isn’t that simple. The primary function of crop scouting is to determine anything unusual or different from the norm and adjust the timing of management actions to the crop growth. Remote sensing can assist with change detection by providing multiple images in the growing season and multiple years of images to compare a field.
Change detection with remote sensing can identify crop issues or differences in vegetation much faster and better than traditional methods. When crop issues are identified, it leads to questions: What is the field evidence telling me? What caused it? Was it seeding depth, germination issues, wireworms, cutworms, nutrient issues, drainage issues, irrigation issues or a combination of factors? Can we fix the problem? What actions are required? Will it pay off? What is the yield difference?
Knowledge always has a cost and it can’t all come from a book. Imagery provides the base knowledge to add layers of information for soils, topography, fertility, vegetation and yield. Precision agronomists have traditional agronomy skills and remote sensing knowledge to use precision agriculture tools. I encourage you to continue learning about precision agriculture technology and seek out good people to assist your farm decisions.