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High-flying satellites - not UAVs - may be first to offer actionable in-season crop imagery beginning this year.
Two tiny Planet Labs satellites float above an International Space Station solar panel after being launched in January. The satellites are part of a planned 100-plus satellite constellation that will be able capture daily images of the entire earth.
UAV sensor imagery options
Near-infrared (NIR) imagery used to create Normalized Difference Vegetation Index (NDVI) crop vigor maps is likely to be the mainstay of unmanned aerial vehicles (UAVs), just as it is in satellite imagery.
But other sensors, including those that precisely measure heat and plant height differences may provide unique opportunities that aren’t possible with satellites.
NDVI maps, which measure crop biomass, provide a window on crop performance as measured by nature’s most perfected environmental sensor – the crop itself. Depending on the time of year, NDVI maps can provide a reading of the crop’s nutrient status, the effects of insect and disease pressure, eventual yield and more.
“There is nothing better than the plant at integrating all the variables affecting growth,” says Bruno Basso, an associate professor at Michigan State University, who is testing a UAV with NIR, thermal and laser-based (lidar) distance sensors under a program funded by Michigan corn growers.
Thermal sensors might provide unique insights that help fine-tune understanding of nutrient and moisture interactions, says Basso. They also could improve irrigation efficiency by generating high-resolution soil moisture maps.
Thermal imagery also could provide an early warning of insect and disease infestations, adds Kevin Price, who recently retired from Kansas State University, where he specialized in remote sensing. “When plants are sick they start running a temperature as the plant’s cooling mechanism is impaired,” he says. “With any kind of insect or disease that attacks the photosynthesis system, you will see anomalous temperatures long before you can see a problem with the human eye. I think thermal imagery could be a game-changer.”
The importance of lidar is less clear-cut, says Basso. The lidar sensor on his UAV will be able to measure crop height differences from plant to plant. In conjunction with NIR and thermal imagery, lidar data may help explain how various stresses affect plant growth, and identify strategies to reduce them.