© ISO 2001 All rights reserved
21
o Push-broom sensor
o Whisk-broom sensor
o Conic scanning sensor
Editors note: This section needs to be reviewed with respect to topics in common with ISO19130.
8.2.3.1.3 Derivable information
Editors note: provides summary of optical remote sensing applications.
8.2.3.2 Passive microwave
8.2.3.2.1 General description
Microwave radiation is Electromagnetic radiation at frequencies above 1 Ghz [derived from IEEE]. Vertically and horizontally polarized measurements are taken for all frequencies.
8.2.3.2.2 Measurements
An imaging radiometer maps the brightness temperature distribution over a field of view FOV. An aperture radiometer does it by scanning the FOV either mechanically or electrically across. Brightness temperature is the measurand.
The temperature equivalent power detected by a radiometer TRAD can be decomposed into several sources. The first source is the brightness temperature TB, defined as the beam averaged thermal emission incident on the
radiometer antenna from the direction of its main beam. TB is itself a component of the antenna temperature TA, which is the beam averaged thermal emission incident on the antenna from all directions. The relationship between TA
and TRAD depends on the method used to calibrate the radiometer. If calibration is referenced to the input of the antenna e.g. by surrounding it by warm or cold absorber loads, then they are equal. If calibration is achieved by
switching the input to the radiometer from the antenna to separate warm or cold loads, then the reference point is the input to that switch. In the latter case, the contribution of TA to TRAD is reduced by hardware losses between the
antenna and the switch, and an additional component of TRAD is contributed by thermal emission from the lossy hardware.
Absolute calibration of a radiometer implies a conversion from measurements of TRAD to estimates of TB TB is then the input to subsequent geophysical data processing and analysis. The conversion from TRAD to TB can be
decomposed according to the sources of TRAD. TA calibration implies conversion from TRAD to TA. This step accounts for thermal emission by and losses due to the radiometer hardware, as noted above, and also corrects for
non-ideal emissionreflection properties of the calibration loads. TB calibration implies conversion from TA to TB. This step is essentially an antenna deconvolution process, which typically involves an estimate of the relative sensitivity of
the antenna within and outside of its main beam, together with an estimate of the thermal emission incident on the antenna outside of its main beam.
8.2.3.2.3 Derivable information
Passive microwave measurements can be used to derive the following geophysical quantities: rainfall, sea surface temperature, vertical water vapor, ocean surface wind speed, sea ice parameters, snow water equivalent, soil surface
moisture.
© ISO 2001 All rights reserved
22
Over land, the standard products include soil moisture, rainfall, and snow cover water content. Geophysical quantities derived from microwave measurements enable investigation of atmospheric and surface
hydrologic and energy cycles. Spatial resolution of passive microwave data is from multiple to 10’s of kilometers
8.2.4 Active sensors
