NASA Scatterometer (NSCAT)provided by NASA
Observation ConceptNASA Scattrometer (NSCAT) is an active microwave radar to measure winds over the oceans by transmitting Ku band microwave pulse (13.995 GHz) and receiving backscatter powers from the ocean surface.
The backscatter powers is subject to changes in direction of surface waves. Multidirectional measurements can thus be used to solve wind speed and direction simultaneously by using algorithm derived from the previous studies.
Antenna Radiation Pattern of NSCAT
As shown in the figure above, NSCAT makes simultaneous measurements of the backscatter powers with three different directions for each side along the track so that wind speed and direction of the sea surface are inferred. The antenna is with a fan beam of 28 degrees (along the direction of beam radiation). The frequency of backscatter powers in changed by Doppler shift.
Planned Missions70% of the entire earth surface is covered with the ocean, which is the largest reservoir on the Earth and contains various thermal elements and greenhouse gases. It is likely that the ocean wind is deeply interrelated with the ocean changes on scales ranging from day to year, and the changes have great effects on climatic and environmental changes. Although the traditional measurements of ocean wind by ships and buoys are limited spatially and temporally, NSCAT has wide instantaneous field of views and makes frequent observation. This observation data will contribute to improvements of numerical weather forecast and ocean circulation model, and a better understanding of thermal balance in the upper ocean and environmental phenomena such as El Nino.
Configuration and Function of SensorNSCAT consists of RF subsystem, antenna subsystem and digital subsystem. The figure below shows configuration of NSCAT at launch.
ADA: Antenna Deployment Assembly
DIU: DC to DC Converter Interface Unit
LRA: Launch Restraint Assembly
REU: Radio Frequency Electronic Unit
The Traveling Wave Tube Amplifier (TWTA) in the RF subsystem produces a radar pulse with 13.995 Ghz (frequency), 5m/sec (width), 62 Hz (repetition frequency). The pulse is fed to each antenna via switch matrix. After the received signals are converted to base band frequency level, they are transmitted to the digital subsystem.
The antenna subsystem consists of six independent fan beam antennas (two pairs of two antennas and two pairs of a single antenna). Each antenna configuration is two array antennas with wave guide slots (each for vertical and horizontal polarization). Two pairs of two antennas use one polarization while the other antennas do both polarization. The antennas will be deployed after launch.
The backscatter powers, of which frequency is changed by Doppler shift, are processed by digital Doppler processor in the digital subsystem, and then transmitted to bus module.
Earth Observation Research Center
Last Update: Last Update: 5 Febrary 1998