Microwave-Photonic Radiometer for Atmospheric Sensing

For many years, microwave radiometers (MWRs) have contributed to the accuracy of atmospheric models, which are used for weather forecasting and climate-change monitoring. In this work, a new MWR architecture is proposed that utilizes the advantages of photonics to measure a wide swath of microwave spectrum from 50 to 70 GHz. An optical-fiber-based arrayed waveguide grating is used to optically process the spectral content from a V-band radio front end. The result is a radiometer that measures the microwave spectrum near the 60 GHz oxygen absorption peak. The instrument described in this work is shown to produce brightness temperature spectra that fit with expected trends for given weather conditions and has a noise equivalent delta temperature of 0.68 K for an integration time of 8.8 s. The microwave-photonic approach to radiometry offers the capability to measure wider spectral bands than accessible using conventional means, and to probe currently unobserved frequencies, within a reasonable form-factor. Further development of the approach outlined in this work will lead to a space-worthy MWR for improved spectral coverage of atmospheric measurements.