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  • 1
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    Comparison of Thermal Coefficients for Two Microwave Detectors (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Laboratory measurements were performed to compare the thermal coefficients of two microwave detectors that might be used for direct detection in L-band radiometers. In particular it was desired to compare the performance of a new-technology flash ADC (analog-to-digital converter) against that of an older-technology diode detector in series with a VFC (voltage-to-frequency converter). The outputs of two state-of-the-art detectors were recorded as a constant 1.414-GHz signal was input and the physical temperatures of the detectors were varied over a range of 10 C. As a further experiment, each detector was tested with a noise diode source and with a sine wave synthesizer source. Thermal coefficients were computed in terms of W/C and in terms of ppt/C at nominal operating temperatures reasonable for the individual devices. Finally, thermal coefficients were calculated in K/C to indicate the change in brightness temperature seen by a theoretical sea surface salinity radiometer employing each detector. The K/C for the flash ADC was determined to be about 2.8 times that of the diode/VFC. Different reactions of the ADC to a noise input and a sine wave input indicated that ADC tests for radiometric purposes, such as this one, should be performed using a noise input.
    Keywords: Instrumentation and Photography
    Type: NASA/TM-2001-211258 , NAS 1.15:211258 , L-18091
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Three Averaging Techniques for Reduction of Antenna Temperature Variance Measured by a Dicke Mode, C-Band Radiometer (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: As new radiometer technologies provide the possibility of greatly improved spatial resolution, their performance must also be evaluated in terms of expected sensitivity and absolute accuracy. As aperture size increases, the sensitivity of a Dicke mode radiometer can be maintained or improved by application of any or all of three digital averaging techniques: antenna data averaging with a greater than 50% antenna duty cycle, reference data averaging, and gain averaging. An experimental, noise-injection, benchtop radiometer at C-band showed a 68.5% reduction in Delta-T after all three averaging methods had been applied simultaneously. For any one antenna integration time, the optimum 34.8% reduction in Delta-T was realized by using an 83.3% antenna/reference duty cycle.
    Keywords: Instrumentation and Photography
    Type: NASA/TM-2000-210283 , L-17987 , NAS 1.15:210283
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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