The TerraRad Tech L-band radiometer is based on space technology from Earth Observation satellites. The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) and the NASA Soil Moisture Active Passive (SMAP) satellites use the same passive remote sensing technique.
Passive microwave remote sensing is another name for the use of microwave radiometers. This technology relies on the fact that many environmental parameters (i.e. soil and vegetation moisture) also alter the microwave signature of these natural materials. Water increases soil’s reflectivity and thus increases the contribution of “cold” space measured at the antenna.
Microwave radiometry is the premier remote sensing technology for soil moisture. Consequently, the European Space Agency SMOS and the NASA SMAP satellites use this technology to monitor global hydrology and soil moisture for weather prediction. Our patented technology can map, from a drone, 5-10 cm depth soil moisture, through crops, with less than 2% error. This provides high resolution maps, enabling practical use cases for agriculture. The system is capable of simultaneously mapping vegetation water content, without saturation observed in other vegetation indices derived from visible and infrared sensors. Our microwave radiometer operates in the 21 cm wavelength (“L-band”) regime of the electromagnetic spectrum.
By measuring the microwave power entering the antenna at two independent polarizations, we calculate the L-band Vegetation Optical Depth (L-VOD) and soil moisture. L-VOD is known to be proportional to crop yield (surface biomass) and to vegetation water content.
The penetration depth of L-band microwaves in soil is between 5 and 10 cm depending on its moisture content. Microwave radiometry is the only remote sensing technique capable of measuring subsurface properties and through thick vegetation.
Microwaves have a significantly longer wavelength than infrared or visible light, which enables these sensors to see through, and into, the earth’s surface. A radiometer is an instrument that measures naturally emitted radiation of very low power levels, similar to a thermal camera, but at a much longer wavelength. The TerraRad Portable L-band Radiometer, or PoLRa, uses a portion of the electromagnetic spectrum reserved only for these passive measurements between 1400 and 1426 MHz.
Satellite-based radiometers lack the ground resolution to view farm-scale data, while radars are hindered by vegetation. Other satellite derived vegetation indices (such as NDVI and Leaf Area Index) do not have the ability to see through crops. Drone-based multi- and hyper-spectral sensors can monitor the top layer of crops, but have no sub-surface measuring capability. TerraRad Tech offers a more proactive approach to crop health as opposed to these reactive methods widely used in the market today. Buried soil moisture probes, also used in agriculture, lack the ability to quantify spatial variability.
Portable L-Band Radiometer: Design and characterization
Published details on the hardware and calibration
The unique and patented dual-polarization antenna array provides two simultaneous and independent measurements. TerraRad’s Portable L-band Radiometer (PoLRa) can be mounted on a UAV (drone), vehicle, or installed on a tower or pole.
The extremely low power consumption (< 5 W) enables the ground-based PoLRa to operate on solar power in remote locations. Use cases of remote ground-based PoLRa systems include Automatic Weather Stations (AWS) and soil moisture ground validation sites.
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