Ocean Vector Wind Measurement Potential from the Global Precipitation Measurement Mission using a Combined Active and Passive Algorithm

Ocean surface vector wind (OVW) is an essential parameter for understanding the physics and dynamics of the ocean-atmosphere system, thereby improving weather forecasting and climate studies. Satellite scatterometers, synthetic aperture radars, and polarimetric microwave radiometers have provided almost global coverage of ocean surface vector wind for the last four decades. Nonetheless, a consistent and uninterrupted long-time data record with the capability of resolving sub-diurnal variability has remained a critical challenge over the years. The Global Precipitation Measurement Mission (GPM) is a satellite mission designed to provide space-based precipitation information on a global scale with complete diurnal sampling. This dissertation presents a combined active and passive retrieval algorithm to investigate the feasibility of ocean surface vector wind measurements from the GPM core satellite by utilizing its Ku- and Ka-band Dual-frequency Precipitation Radar (DPR) and the multi-frequency GPM Microwave Imager (GMI) observations. The unique GPM active and passive geophysical model functions were empirically developed by characterizing the anisotropic nature of ocean backscatter of normalized radar cross-section (δ°) and brightness temperature (TB) at multiple bands. For passive GMF, the modified 2nd Stoke\u27s parameter (linear combination of V and H-pol TBs) was used to mitigate the atmospheric contamination and to enhance the anisotropic wind direction signal superimposed on GMI TBs. The GMFs were combined in a maximum likelihood estimation (MLE) algorithm to infer the OVW. Finally, the retrieval algorithm was validated by comparing OVW retrievals with collocated NASA Advanced Scatterometer (ASCAT) wind vectors. The wind speed and direction retrieval performance statistics are promising and comparable with those of conventional scatterometer and polarimetric radiometer data products. The algorithm demonstrates the capability of the GPM to provide a long-term OVW data record for the entire GPM-TRMM era, which may include unique monthly diurnal OVW statistics

Polarimetric Microwave Radiometer Calibration.

A polarimetric radiometer is a radiometer with the capability to measure the correlation information between vertically and horizontally polarized electric fields. To better understand and calibrate this type of radiometer, several research efforts have been undertaken. 1) All microwave radiometer measurements of brightness temperature (TB) include an additive noise component. The variance and correlation statistics of the additive noise component of fully polarimetric radiometer measurements are derived from theoretical considerations and the resulting relationships are verified experimentally. It is found that the noise can be correlated among polarimetric channels and that the correlation statistics can vary as a function of the polarization state of the scene under observation. 2) A polarimetric radiometer calibration algorithm has been developed which makes use of the Correlated Noise Calibration Standard (CNCS) to aid in the characterization of microwave polarimetric radiometers and to characterize the non-ideal characteristics of the CNCS itself simultaneously. CNCS has been developed by the Space Physics Research Laboratory of the University of Michigan (SPRL). The calibration algorithm has been verified using the DetMit L-band radiometer. The precision of the calibration is estimated by Monte Carlo simulations. A CNCS forward model has been developed to describe the non-ideal characteristics of the CNCS. Impedance-mismatches between the CNCS and radiometer under test are also considered in the calibration. 3) The calibration technique is demonstrated by applying it to the Engineering Model (EM) of the NASA Aquarius radiometer. CNCS is used to calibrate the Aquarius radiometer – specifically to retrieve its channel phase imbalance and the thermal emission characteristics of transmission line between its antenna and receiver. The impact of errors in calibration of the radiometer channel phase imbalance on Sea Surface Salinity (SSS) retrievals by Aquarius is also analyzed. 4) The CNCS has also been used to calibrate the Breadboard Model (BM) of the L-band NASA Juno radiometer. In order to cover the broad TB dynamic range of the Juno radiometer, a special linearization process has been developed for the CNCS. The method combines multiple Arbitrary Waveform Generator gaussian noise signals with different values of variance to construct the necessary range of TB levelsPh.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61741/1/jzhpeng_1.pd