We are developing a new remote sensing system at the University of Arizona called the Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS). ATOMMS combines many of the best features of GPS Radio Occultation (RO) and the Microwave Limb Sounder (MLS) by actively probing cm to sub-mm wavelength atmospheric absorption features via satellite-to-satellite occultation. ATOMMS will provide an unprecedented combination of features for monitoring climate from orbit. With funding from NSF and aircraft time from NASA, we will demonstrate the ATOMMS concept via high altitude aircraft-to-aircraft occultations in 2011. Here we summarize the ATOMMS concept and demonstration project and provide early test results from the instrument indicative of ATOMMS capabilities and performance.

Describes the design and construction of an 8000 m/sup 2/ 74-MHz phased array dedicated to measurement of the solar-wind velocity using the interplanetary scintillation (IPS) technique, and a simple and novel autocalibration system that measures and connects phase and amplitude errors to a level of 1/spl deg/ and 0.2 dB rms. In the IPS technique, intensity fluctuations of compact radio sources caused by plasma turbulence in the solar wind are observed with multiple antennas. The time lag between the antennas is estimated using a cross-correlation analysis. The primary requirement of such a system is sensitivity so that one may observe a large number of compact sources. A secondary requirement is high beam efficiency so that one may observe near the Sun. The scan angle was limited to allow the largest possible array element and thus the simplest feed system. The feed was designed to have independent phase and amplitude control of each element. Although this is not strictly necessary it permits the use of the feed as a phase switched interferometer with which any element can be correlated against any other group of elements. This provides a simple and accurate calibration of the entire array. The antenna was completely prefabricated, the site preparation was minimal, and the installation was quick and accurate. The system is remotely operated. The control information, system diagnostics, and data are transmitted over a leased telephone line. The entire system is powered by storage batteries charged by solar cells. In addition to IFS it has been used extensively for pulsar observations which have similar requirements.>

Calculations of the exact Cramer-Rao bound (CRB) for unbiased estimates of the mean frequency, signal power, and spectral width of Doppler radar/lidar signals (a Gaussian random process) are presented. Approximate CRBs are derived using the discrete Fourier transform (DFT). These approximate results are equal to the exact CRB when the DFT coefficients are mutually uncorrelated. Previous high SNR limits for CRBs are shown to be inaccurate because the discrete summations cannot be approximated with integration. The performance of an approximate maximum likelihood estimator for mean frequency approaches the exact CRB for moderate SNR and moderate spectral width.>