Doppler Scatterometry

NASA’s DopplerScatt instrument (Rodriguez et al., 2018) provides simultaneous measurements of ocean vector winds and surface currents estimates over a 24-km swath. The surface currents are used to compute surface convergence and vorticity. Winds are used to investigate air-sea interaction and to estimate the wind-driven current component.

DopplerScatt uses a pencil-beam mechanically scanning antenna that measures surface radar cross sections and radial Doppler velocities that are processed to estimate ocean vector winds and currents concurrently. The instrument operates at Ka-band (35.75 GHz), allowing for a compact antenna accommodation using waveguide slot array technology (22 cm diameter) protected by the RF-transparent radome (Fig. 3.1). The antenna rotation enables wide swath coverage (24 km when flying at 28 kft) as well as looks in multiple azimuth directions allowing the recovery of vector winds and surface currents at 200 m spatial resolution. Unlike traditional scatterometers, the radar operates coherently allowing for Doppler measurements of the relative velocity between the platform and the surface. DopplerScatt includes a precision Inertial Measurement Unit (IMU) coupled with the Applanix GPS receiver which enables accurate motion compensation and removal of the platform velocity for retrieval of the surface velocity component.

DopplerScatt was developed under NASA Earth Science and Technology Office (ESTO) Instrument Incubator Program (IIP) and NASA AITT.

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High Altitude Imaging Wind and Rain Airborne Profiler

HIWRAP (High-Altitude Imaging Wind and Rain Airborne Profiler) is a dual-frequency radar (Ka- and Ku-band), dual-beam (300 and 400 incidence angle), conical scan, solid-state transmitter-based system, designed for operation on the high-altitude (20 km) Global Hawk UAV. HIWRAP characteristics: Conically scanning; Simultaneous Ku/Ka-band & two beams @30 and 40 deg; Winds using precipitation & clouds as tracers; Ocean vector wind scatterometry; Map the 3-dimensional winds and precipitation within hurricanes and other severe weather events; Map ocean surface winds in clear to light rain regions using scatterometry.

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Polarimetric Ku-Band Scatterometer

PolSCAT is a Ku-band polarmetric scanning scatterometer operating at 13.95 GHz. with an approved NASA license. The transmitting polarizations of PolSCAT, alternating between Vertical and Horizontal, from pulse to pulse. Two receivers detect the V and H polarized radar echoes simultaneously allowing for measurements of VV, HH, VH, and HV radar responses. It provides scalable resolution, between 3,000 and 20,000 feet AGL.

The PolSCAT antenna assembly includes two axis gimbals for conically scanning, parabolic antenna, which is controlled from 0° (nadir) to 65 degrees. It was designed and built to investigate the benefits of active microwave for the remote sensing of high resolution snow-water-equivalent (SWE).

PolSCAT’s flexible design is compatible with many aircraft. It has flown on the NCAR C-130, NASA’s DC-8, P-3, and Twin Otter International’s, Twin Otter. Flown more than 500 hours in support of NASA’s Cold Land Process (CLPX) campaigns, PolSCAT is a very mature instrument.

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Passive Active L- and S-band Sensor

PALS is a combined polarimetric radiometer and NASA licensed radar sharing a rotating planar array antenna. The PALS instrument includes a combined L-band radiometer and scatterometer , operating at 1.413 GHz and 1.26 GHz respectively. It was designed and built to investigate the benefits of combining passive and active microwave sensors for Ocean salinity and Soil moisture remote sensing. It is the prototype for the Aquarius and SMAP missions and its flexible design is compatible with many aircraft.

The PALS radar and radiometer time share a dual pole, dual frequency planner array antenna. The antenna configuration can be fixed or rotating. It provides scalable resolution, between 3,000 and 20,000 feet AGL. It is an Aquarius and SMAP test bed.

PALS has flown on the NCAR C-130, NASA’s P-3 and Twin Otter International’s, Twin Otter. It is a very mature instrument, and has flown more than 800 hours, in support of NASA campaigns.

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