Today’s agricultural industry is a sharp contrast to yesteryear, when farmers wished for better and cheaper mechanization, and information reconnaissance meant walking fields, eyeing crops and probing the soil with bare hands to determine moisture levels. Modern agribusiness is still about sight, touch and feel, but professionals acquire their crop sense from mechanization and information technology that go far beyond self-propelled combines, fertilizer spreaders and yield monitors.
 

Mechanization in agriculture now means satellites, Global Positioning System (GPS) receivers, laptops and personal digital assistants, supplemented by precision agriculture software and geographic information systems. Information reconnaissance equates to grabbing a mouse, accessing the Web, viewing satellite imagery, weather reports and commodity prices, and creating customized maps of field boundaries, crop vigor, yield and fertilizer spread.
 

Satellite imagery in particular has become a crucial source of sight for many agriculture professionals who need to effectively plan, perform, monitor and analyze operations. Although optical imagery has been, and still is, the predominant source of remote intelligence for monitoring agricultural activities, radar satellites—particularly C-band Synthetic Aperture Radar (SAR) satellites such as Canada’s RADARSAT-1—are finding a niche in this arena. With the ability to provide unique information about crop structure and moisture content, coupled with day-and-night imaging capability regardless of weather, SAR satellites are becoming an important source of remote intelligence for agricultural professionals.
 

For example, RADARSAT-1 projects have helped scientists develop a system to predict and minimize the risk of locust outbreaks in Kazakhstan, and aided growers and insurers in assessing the aftermath of storm damage to crops in Canada. Based on such success, researchers and business developers are convinced that the radar picture for agricultural applications will grow even brighter when RADARSAT-2 is operational (see “RADARSAT-2 Launch Slated for Late 2005,” below).
 

“RADARSAT-2 will be a significant step forward for agriculture,” says Heather McNairn, a research scientist with Agriculture and Agri-Food Canada (AAFC) who has studied the applications of satellite data for agriculture for the last 15 years. “The [all-weather] reliability of radar … and its sensitivity to surface roughness, moisture and crop structure represent significant advantages over optical systems. With the sensor advancements of RADARSAT-2—particularly the availability of multipolarized data—a single image will provide much more information. So for projects like mapping crop type, I think it will be possible to reach the point where we’ll be able to map with radar data alone, minimizing the need for optical data.”

Raising the Radar Bar

Scheduled for launch in late 2005, RADARSAT-2 will offer several enhancements compared with RADARSAT-1, ranging from improvements in resolution to full flexibility in the selection of polarization options (see “Polarized Waves—Scientists Search for the Right Combination,” below). RADARSAT-2’s imaging instrument will provide SAR imagery at horizontal, vertical and cross polarization across a range of resolutions from 3 meters to 100 meters, with swath widths ranging from 20 kilometers to 500 kilometers. In addition to continuing to deliver all RADARSAT-1 imaging modes, RADARSAT-2 will provide the imaging modes to the right and left side of the satellite track, improving revisit times.

Fielding the Agricultural Scene

To better understand Canada’s vast croplands and rangelands, AAFC scientists are developing an operational agriculture mapping system that will integrate a variety of data sources, including optical and radar imagery. Producing better land-cover maps, crop maps and maps of land-management practices is part of AAFC’s Agricultural Policy Framework strategy to increase the awareness, understanding and recognition of agriculture’s relationship to the environment.
 

Beginning in 2006, crop maps and maps of land-management activities—specifically tillage practices—will be produced and updated every year. Land-cover maps will be updated every five years. According to McNairn, the plan is to use RADARSAT-2 and U.S. Landsat or French SPOT satellites as the core data sources to create the information products.

“For the land-cover product, we will predominantly use Landsat or SPOT, because we can build up our knowledge of land cover during a 5-year period,” she explains. “But because the crop and tillage information is required on a yearly basis, the optical imagery isn’t reliable enough due to cloud-cover issues. We’re really interested in radar to create these information products, because we can be guaranteed that we’ll receive timely data.”
 

Eventually the information will be offered to the public through AAFC’s National Land and Water Information System. Early benefactors of the satellite-derived information will be the National Agri-Environmental Health Analysis and Reporting Program (NAHARP) and the National Carbon and Greenhouse Gas Accounting and Verification System (NCGAVS). NAHARP is designed to enable personnel to link agrienvironmental indicators such as erosion and soil contamination with, for example, economic information to project future environmental outcomes and assess current and planned programs and policies. NCGAVS seeks a better understanding of Canada’s carbon resources—specifically whether agricultural land can be used as carbon sinks—to supply solid information to the Kyoto Protocol initiative.* Both programs stand to benefit from products developed from radar and optical imagery.
 

In anticipation of RADARSAT-2, McNairn and her colleagues have been researching the satellite’s potential use for various agriculture applications. Of utmost importance is to assess the viability of the radar imagery as a core contributor to AAFC’s mapping activities. Using airborne SAR data acquired by Environment Canada’s CV-580 aircraft, NASA’s Shuttle Imaging Radar-C instrument and the ENVISAT ASAR sensor, researchers have focused on three primary agriculture applications: crop information (mapping crop types and determining crop conditions), estimating and mapping soil moisture, and mapping soil tillage and crop residue cover.

According to the results, RADARSAT-2 shows promise for all three application areas. Because radar is sensitive to differences in crop structure, individual crops such as wheat, canola, soybeans and alfalfa will produce different radar responses, allowing good contrast among crop types. Cross-polarizations—the single most important polarization for crop discrimination—have been found to be particularly useful for categorizing crops. For example, at a test site in Altona, Manitoba, an HV channel clearly distinguished canola, flax, wheat and sugarbeet crops from each other. Using V-polarized waves researchers also could determine differences in crop structure due to changes in the crop’s growth or health.
 

Because C-band radar is sensitive to moisture and can penetrate the soil of a bare field, it is useful for estimating moisture content within the first few centimeters of soil. However, radar’s affectability by moisture and surface roughness has made it challenging for RADARSAT-1 users to determine if bright areas on an image are due to wetness or roughness. With RADARSAT-1’s single polarization, it is impossible to separate the effects of surface moisture from roughness using a single image. With RADARSAT-2, however, scattering models can use multipolarizations to resolve soil moisture and surface roughness.
 

Research also indicates that as fields are tilled, the increase in soil surface roughness results in a backscatter increase, as do fields that are covered with substantial post-harvest crop residue. Both conditions are captured distinctly by cross-polarized waves.
 

According to McNairn, the results from these studies served as the catalyst for AAFC’s interest in using RADARSAT-2 in its mapping activities.
 

“I don’t think we’ll be able to deliver crop maps on an annual basis without radar data,” she concludes. “The optical data aren’t reliable enough. The operational system we’re developing will integrate optical and radar, but I don’t think we’ll be successful, or operational, without the radar data. For the land-management mapping, we hope to map tillage with radar–because roughness is a driving factor for radar–and we hope to map residue amounts with optical data and combine that information to actually derive conservation practices.”

Canada is too massive to map crops and land-management activities annually on a nationwide scale, so AAFC is devising an array of sites that represent the country’s agricultural diversity to develop its mapping methodologies and serve as continual monitoring sites. Radar, optical and ground data already are being collected at two pilot sites in Eastern Ontario and Lethbridge, Alberta.
 

Mapping Damage and Moisture
Interest in RADARSAT-2 applications also can be found scattered throughout corporate research and development departments.  Saskatchewan-based Digital Environmental (DE) is conducting studies on the potential to use

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