Remote sensing — the use of spacebased satellite technologies to obtain information on environmental variables — in combination with other types of data, can provide information on changes in the Earth’s surface and atmosphere that are critical for weather forecasting and responding to human welfare issues (disease outbreaks, food shortages, and floods). Satellites and other remote sensing tools have gathered a great deal of useful data on the Earth’s climate systems, drainage systems, geologic structures, thermal anomalies, geomorphologic features, and distribution of vegetation.

A software-defined radiometer will be able to scan multiple radio frequency bands (L–K, up to 200-MHz bandwidth) using the same receiver architecture. This will be beneficial to future missions because environmental information and data can be analyzed (RFI mitigation, ground validation, RFI surveying, and RH research) for an entire frequency band instead of a subset (SMAP: 1400–1427 MHz). This will also eliminate the redundancy of designing multiple radiometer front ends, which will decrease hardware expenses, development time, and overall budget.

The radiometer will output horizontal and vertical polarization signals and their intermediate frequency representation. The software-defined radiometer will have a local oscillator (LO) multiplexer that contains N mixer frequencies, as well as a bandpass filter multiplexer that contains N 200-MHz bandpass filters. The N filters are determined by the specific frequency band’s bandwidth and the LO that creates the center frequency within that chosen band. They both will be controlled by an analog switch. This output will be sent to a digital back-end that will digitize the signal, perform baseband conversion with a programmable digital mixer, and perform unique algorithmic functions.

The first step is to finalize the part selection with the programmable frontend components. The programmable LO and bandpass filters would be incorporated into the L-band radiometer. The current GREX radiometer will be used as a blueprint. Radiometer signal processing algorithms will be simulated in MATLAB, and once tested and validated, FPGA implementation will begin. The final algorithm will be implemented on the digital back-end system and integrated with the RF front-end.

This work was done by Lynn R. Miles, Damon C. Bradley, Englin Wong, Edward Kim, and Jeffrey Piepmeier of Goddard Space Flight Center; and Peter H. Young of Sigma Space. GSC-16976-1

NASA Tech Briefs Magazine

This article first appeared in the January, 2016 issue of NASA Tech Briefs Magazine.

Read more articles from this issue here.

Read more articles from the archives here.