Microwave Photonic Radiometers for Weather Forecasting and Situational Awareness

Passive Microwave Remote Sensing is currently utilized by AFRL, NASA, NOAA, and others to conduct Earth Science missions, including weather forecasting, early warning systems, and climate studies. Soundings of the atmosphere are conducted near several oxygen and water absorption lines at frequencies of ~20-200 GHz to determine key parameters of the atmospheric state, including temperature and humidity profiles. To improve retrieval accuracy of these parameters as well as predictive ability of weather models, a large number of closely spaced frequencies, i.e. hyperspectral sensing is needed. As such, PSI will develop a hyperspectral microwave radiometer sounder capable of acquiring a hundred or more detection frequencies simultaneously on a <1 GHz channel spacing. We leverage microwave photonics to convert the radio frequency signals to optical frequencies, where they are readily manipulated with low loss and wide bandwidth using optical components and detected using an optical spectrometer back-end. Under the proposed effort, we extend our existing radiometer hardware to enable concurrent, spectrally resolved measurements of the sky brightness temperature in the frequency range of 50-75 GHz, at the oxygen absorption line. We demonstrate a 16-channel system with 1.6 GHz channel spacing that can be scaled to larger channel counts in a straightforward manner.