Abstract
A low-mass and low-volume dual-polarization L-band radiometer is introduced that has applications for ground-based remote sensing or unmanned aerial vehicle (UAV)-based mapping. With prominent use aboard the ESA Soil Moisture and Ocean Salinity (SMOS) and NASA Soil Moisture Active Passive (SMAP) satellites, L-band radiometry can be used to retrieve environmental parameters, including soil moisture, sea surface salinity, snow liquid water content, snow density, vegetation optical depth, etc. The design and testing of the air-gapped patch array antenna is introduced and is shown to provide a 3-dB full power beamwidth of 37°. We present the radio-frequency (RF) front end design, which uses direct detection architecture and a square-law power detector. Calibration is performed using two internal references, including a matched resistive source (RS) at ambient temperature and an active cold source (ACS). The radio-frequency (RF) front end does not require temperature stabilization, due to characterization of the ACS noise temperature by sky measurements. The ACS characterization procedure is presented. The noise equivalent delta (Δ) temperature (NEΔT) of the radiometer is ~0.14 K at 1 s integration time. The total antenna temperature uncertainty ranges from 0.6 to 1.5 K.
Highlights
The modern age of space-borne L-band (1–2 GHz) microwave radiometers began with the European Space Agency (ESA) Soil Moisture and Ocean Salinity Satellite (SMOS) [1] in 2010
This was followed by the National Aeronautics and Space Administration (NASA) satellites Aquarius [2] and Soil Moisture Active Passive (SMAP) [3]
We have introduced a small, low-mass, and cost-effective L-band radiometer design, and provided characterization results to demonstrate its performance
Summary
The modern age of space-borne L-band (1–2 GHz) microwave radiometers began with the European Space Agency (ESA) Soil Moisture and Ocean Salinity Satellite (SMOS) [1] in 2010. UAV-based L-band radiometers have been demonstrated previously in [16,17] Neither of these systems provide dual-polarization off-nadir antenna temperatures which are optimal for use with established retrieval algorithms such as the Tau-Omega (TO) [18,19] or Two-Stream (2S) emission models (EMs) [5]. The PoLRa is a direct-detection radiometer providing calibrated dual-polarization L-band antenna temperatures with resolution of ~0.14 K at 1 s integration, and total uncertainty ranging between 0.6–1.5 K, depending on integration time and input antenna temperature. Initial results include drone-based antenna temperature measurements and soil moisture retrievals
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