A correlated-noise source has been developed for use in calibrating an airborne or spaceborne Earth-observing correlation microwave polarimeter that operates in a pass band that includes a nominal frequency of 10.7 GHz. Deviations from ideal behavior of the hardware of correlation polarimeters are such as to decorrelate the signals measured by such an instrument. A correlated- noise source provides known input signals, measurements of which can be processed to estimate and correct for the decorrelation effect.
Typical prior correlated-noise sources suitable for this purpose consist of multiple units connected by coaxial cables; as such, they tend to be too bulky and heavy to be incorporated into flight instrumentation assemblies. In contrast, the present correlated-noise source is a single unit (see figure) that is relatively compact and can easily be integrated into a flight instrumentation assembly. The unit includes directional couplers for sampling noise-diode outputs and injection of test signals. This source provides both correlated (sum) and anticorrelated (difference) signal components at the output ports. The source can be operated in four modes: (1) both noise diodes on, (2) both noise diodes off, (3) noise diode 1 on with noise diode 2 off, and (4) noise diode 2 on with noise diode 1 off. Measurements of the resulting combinations of correlated and anticorrelated signal components provide the data needed for calibration.
This work was done by Jeffrey R. Piepmeier and Edward J. Kim of Goddard Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/Computers category. This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Goddard Space Flight Center
Refer to GSC-14745-1.