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Develop Prototype Hyperspectral Microwave Imager for Terrestrial Weather

Description:

TECHNOLOGY AREA(S): Sensors 

OBJECTIVE: Development of a prototype hyperspectral microwave sensor which significantly increases the bandwidth and line channel spatial wavenumber density of space-based passively-measured microwave radiances emitted and transmitted through the earth's atmosphere. The anticipated products of the prototype hyperspectral microwave sensor include improved accuracy and diagnosis and prediction of 3-D radiative transfer through optically-thick clouds which can assist missile launch plume detection in the presence of sunlit-clouds. 

DESCRIPTION: Modern passive microwave space-borne sensors have a limited number of channels available, totaling between 5 and 30 channels. This limited number of channels has been shown to be insufficient to solve for the ill-posed nature of the inversion of the geophysical state from space-borne measurements. This is especially true for cases where cloud, rain and/or ice are present in the atmosphere. In this case, a large uncertainty exists due the lack of knowledge about the particle density, shape, size distribution, vertical structure, and temperature dependence. A larger number of channels will help solve for the inherent ambiguities in these cases. This will also provide (1) a higher vertical resolution for the temperature and humidity sounding in all-weather conditions, (2) a better distinction between the surface and the atmospheric signals leading to retrievals of ocean wind vectors, snow and ice, soil moisture, (3) better surface typing due to the different spectral signatures associated with the different surface parameters mixtures, and (4) a better characterization of the microwave spectroscopic parameters (line width, line strength, line shape, frequency shift). While sensors operating in the infrared, short wave infrared, and near-infrared have experienced an ever increasing number of channels and bands with the new hyperspectral sensors, microwave sensors -- despite their large proven benefits to numerical weather prediction and their ability to penetrate cloud and sense within and below the cloudy and rainy layers -- have not seen their number of channels increase, mainly due to technological challenges. This type of sensor would be expected to have significant positive impacts on the forecast skills of numerical weather prediction models due to the increase in sounding retrievals,, especially if deployed in space with large spatial and temporal coverages. This improvement is expected in medium-range weather forecasts as well as in the nowcasting/short-term forecasting of mesoscale events. Besides the large number of channels (between hundreds and thousands) sought, in a range between 6 GHz and 300 GHz, it is emphasized that the noise level should be as low as possible and at least as low as current state of the art sensors by taking advantage of the new developments in radiometry technology. 

PHASE I: Define what is meant by "hyperspectral microwave" in terms of frequency, wavenumber, and wavelength differentials, including the total number of channels. Develop a prototype hyperspectral microwave sensor design to include expected signal-to-noise ratio, radiance levels, channel or band spatial wave-number spacing, and applicable observing system simulation experiments (OSSE) in order to assess the impact of additional spectral channels and bandwidth on numerical weather prediction accuracy. 

PHASE II: Build a prototype hyperspectral microwave sensor based on the design approved in phase I employing the most recent technological advances as appropriate. Conduct phased sensor tests including on-ground, tower borne, and airborne tests. Refine data assimilation techniques for ingestion of the hyperspectral measurements into 3-D cloud forecast models such as those developed at the 557th Weather Wing. 

PHASE III: Apply the space-based hyperspectral microwave sensor towards military applications including 3-D global cloud diagnoses and forecasts, and surface snow and ice cover for ISR and Missile Warning. Civilian applications potentially include improved aviation weather hazard and in-flight forecasts and medium range weather prediction. 

REFERENCES: 

1. Blackwell, W.J., L.J. Bickmeier, R.V. Leslie, M.L. Pieper, J.E. Samra, C. Surussavadee, and C.A. Upham, 2011: Hyperspectral microwave atmospheric sounding. IEEE Transactions on Geoscience and Remote Sensing, 49, 128-142; 2. Townes, C.H., and A.L. Schawlow, 1975: Microwave Spectroscopy. Dover, New York, 699 pp.; 3. Rothman, L.S., et al, 2013: The HITRAN2012 molecular spectroscopic database. Journal of Quantitative Spectroscopy and Radiative Transfer, 130, 4-50.; 4. Liu, Q., and F. Weng, 2002: A microwave polarimetric two-stream radiative transfer model. Journal of the Atmospheric Sciences, 59, 2396-2402.

KEYWORDS: Molecular Spectroscopy, Emissivity, Polarization, Radiative Transfer, Transmission, Reflection, Absorption, Microwave Imagery, Microwave Soundings, Weighting Functions 

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