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... > Instruments > Earth Remote Sensing Instruments > Active Remote Sensing > Altimeters > Radar Altimeters > ALT (SEASAT 1)

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ALT (SEASAT 1)  

Definition

  • The Radar Altimeter (ALT) experiment measured (1) the spacecraft height above mean sea level and (2) the significant wave height and backscatter coefficient of the ocean surface beneath the spacecraft. The altimeter was a more accurate version of the Skylab Radar Altimeter, and was similar to the altimeter flown on GEOS 3. Two of its unique features were a linear FM transmitter with a 320-MHz bandwidth, which yielded a 3.125-ns time-delay resolution, and microprocessor-implemented closed-loop range tracking, automatic gain control, and real-time estimation of significant wave height. The instrument operated at 13.5 GHz using a 1-m parabolic antenna pointed at nadir and had a swath width which varied from 2.4 to 12 km, depending on sea state. The precision of the height measurement was 10 cm (rms). The estimate of significant wave height was accurate to 0.5 m or 10%, whichever was greater, and the ocean backscatter coefficient had an accuracy of 1 dB. For a more detailed description, see W. Townsend, "An initial assessment of the performance achieved by the Seasat-1 radar altimeter," IEEE J. of Oceanic. Eng., v. OE-5, pp. 80-92, 1980. The ALT was turned on for the first time on July 3, 1978, and declared operational on July 7, 1978. The ALT operated successfully until October 10, 1978, when the spacecraft prematurely terminated the mission. Data are available from SDSD. Summary provided by http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1978-064A-01 Group: Instrument_Details Entry_ID: ALT (SEASAT 1) Group: Instrument_Identification Instrument_Category: Earth Remote Sensing Instruments Instrument_Class: Active Remote Sensing Instrument_Type: Altimeters Instrument_Subtype: Radar Altimeters Short_Name: ALT (SEASAT 1) Long_Name: SEASAT 1 Radar Altimeter End_Group Group: Associated_Platforms Short_Name: SEASAT 1 End_Group Online_Resource: http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1978-064A-01 Creation_Date: 2009-07-02 End_Group (en)

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https://gcmd.earthdata.nasa.gov/kms/concept/44dbfc87-9835-4093-9aac-33231ccdd990

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