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Proceedings Paper

Time-Delay-And-Integration Charge Coupled Devices (CCDs) Applied To The Thematic Mapper
Author(s): Leslie L. Thompson; David H. McCann
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Paper Abstract

The Thematic Mapper (with its 30 m ground footprint in five-spectral bands from 0.4 μm to 2.0 μm and 120 m GFT in a 10.5 μm to 12.5 μm spectral band) represents the next generation sensor system for application to earth resource survey. The Thematic Mapper (TM) uses a 56 cm x 42 cm oscillating mirror to scan the scene, and is designed to provide accurate radiometric measurements. Currently, in the visible focal plane the discrete detectors must provide 80% quantum efficiency, nominally 100 electrons noise, less than 5% ripple in the spectral response, and 0.5% signal crosstalk to meet system requirements. This focal plane uses complex hybrid assembly techniques to interface silicon photodiodes to JFET preamplifiers. This complexity can be ameliorated by using a new approach in signal pro-cessing which takes advantage of the properties of charge-coupled devices (CCD). A 20-channel time-delay-and-integration (TDI) CCD with nine stages of integration per channel has been built for a TM application. By going to a CCD array which operates in a TDI mode, over 700 individual Op Amps can be replaced with only 48 Op Amps. Smooth spectral response and 70% quantum efficiency have been provided by using doped tin oxide gates over the imaging region. The 20 x 9 TDI device when operated with all 9 integration stages, ,exceeded SNR requirements by a factor of 2. The crosstalk performance is controlled by providing high charge transfer efficiency using a buried channel CCD. The TDI device has demonstrated charge integration for both forward and reverse scans of the oscillating mirror, and a form of exposure control is provided by integrating over 3, 6, or all 9 stages in either direction of scan.

Paper Details

Date Published: 15 September 1978
PDF: 8 pages
Proc. SPIE 0143, Applications of Electronic Imaging Systems, (15 September 1978);
Show Author Affiliations
Leslie L. Thompson, NASA/Goddard Space Flight Center (United States)
David H. McCann, Westinghouse Advanced Technology Laboratory (United States)

Published in SPIE Proceedings Vol. 0143:
Applications of Electronic Imaging Systems
Richard E. Franseen; Dieter K. Schroder, Editor(s)

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