Accurate models for atmospheric propagation are necessary to derive operational data products from GNSS remote sensing measurements. A laboratory system has been developed to make direct measurements of the refractivity and absorptivity of atmospheric gases at GPS L1 and L2 frequencies. The laboratory system consists of a cylindrical microwave resonator housed within an environmental chamber and is designed for measurements at temperatures and pressures relevant to the Earth's atmosphere. We present measurements of the Debye absorption of oxygen from 1.2-2.3 GHz at pressures of 200-1000 Torr and at temperatures from 290-350 K. These measurements are applicable to the modeling of L band atmospheric opacity in the context of GNSS radio occultation experiments.

Early seminal contributions by Staelin helped initiate the field of microwave remote sensing as a key tool for the study of planetary atmospheres. Recent studies of the microwave emission from the neutral atmosphere of Venus have been used to identify the abundance and spatial distribution of microwave absorbing constituents such as sulfuric acid vapor and sulfur dioxide. A new mission to Jupiter, called Juno, will employ a six-channel microwave radiometer to measure the abundance and distribution of ammonia and water vapor in the Jovian atmosphere.

The increasing usage of radio spectrum in both frequency and power, coupled with the vulnerability of passive remote sensing systems to interference, necessitates a better understanding of the existing and predicted usage of the spectral environment. A Radio Spectrum Evaluation System (RSES) has been developed which provides coverage from 400 MHz to 7.2 GHz and offers the capability to observe and analyze spectral usage in multiple dimensions: frequency, power, location space, azimuth, polarization and time. Since passive radiometry can suffer interference at extremely low power levels, this system's sensitivity has been enhanced by reducing intermodulation distortion and thermal noise. A study of the radio frequency usage in and adjacent to the remote sensing bands at 4.5 cm and 21 cm was undertaken to determine current usage levels and characteristics. These bands are of interest to instruments such as NPOESS/CMIS and ESA/SMOS. While this study was performed in an urban area, additional studies are measuring spectrum usage in suburban and rural environments to assist in predicting future spectral usage and characteristics

An increasing number of commercial applications are being promoted for future Ka-band satellite communication systems. Many of these systems will involve low-margin very small aperture terminals (VSATs). These systems are subject to important atmospheric propagation degradations that affect the quality of transmission and the link availability. The objective of this paper is to characterize the Ka-band channel and evaluate the performance degradation in VSATs resulting from atmospheric propagation, impairments. In particular microwave propagation through a turbulent atmosphere is discussed, and the statistical characterization and modeling of tropospheric scintillation is reviewed. Moreover, the paper extends the method proposed by Filip and Vilar (1990) for the long-term characterization and modeling of the combined effect of rain impairments and scintillation. Specifically, the increase in noise temperature during rain events is added to the Filip-Vilar model. This leads to a five-parameter global fading distribution that is used to predict typical Ka-band satellite link outage time, the mathematical formalism is illustrated by applying the method to the selected case of the Advanced Communications Technology Satellite (ACTS)-Georgia Tech experimental downlink. Numerical results confirm that both rain impairments and scintillation are important factors in the design of Ka-band VSAT systems.