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SCATSAT-1 Payloads

The scientific payload contains the Scanning Scatterometer (SCAT) instrument.

Scanning Scatterometer (SCAT)

scat observation

SCAT is an active microwave device designed and developed at SAC/ISRO, Ahmedabad. It is used to determine ocean surface level wind vectors through estimation of radar backscatter. The scatterometer system has a 1-m parabolic dish antenna and a dual feed assembly to generate two pencil beams and is scanned at a rate of 20.5 rpm to cover the entire swath. The Ku-band pencil beam scatterometer is an active microwave radar operating at 13.515 GHz providing a ground resolution cell of size 25 x 25 km. The parabolic dish antenna of 1 meter diameter is offset mounted with a cant angle of about 46 degree with respect to earth viewing axis. This antenna is continuously rotated at 20.5 rpm using a scan mechanism with the scan axis along the +ve Yaw axis. By using two offset feeds at the focal plane of the antenna, two beams are generated which will conically scan the ground surface. The back scattered power in each beam from the ocean surface is measured to derive wind vector. The inner beam makes an incidence angle of 48.900 and the outer beam makes an incidence angle of 57.600 on the ground. It covers a continuous swath of 1400 km for inner beam and 1840 km for outer beam respectively. The inner and outer beams are configured in horizontal and vertical polarization respectively for both transmit and receive modes. The aim is to provide global ocean coverage and wind vector retrieval with a revisit time of 2 days.

Parameter Inner beam Outer beam
Orbital altitude 720 km
Instrument frequency 13.515 GHz (Ku-band)
Wind speed range 3-30 m/s, accuracy of 1.8 m/s (rms) or 10%
Wind direction 00 to 3600, accuracy of 200 rms
Wind vector cell size (resolution) 25 km x 25 km grid
Polarization HH VV
Swath width 1400 km 1840 km
Scanning circle radius 700 km 920 km
Scanning rate 20.5 rpm