John R. Rowland

A Tutorial Assessment of Atmospheric Height Uncertainties for High-Precision Satellite Altimeter Missions to Monitor Ocean Currents

A large body of information from a number of sources is brought together and an error budget is deduced giving the projected overall height uncertainty correction for a suggested next generation high-precision radar altimeter. Uncertainties introduced by the wet and dry troposphere, clouds, and the ionosphere are reviewed. A suggested next-generation precision altimeter is assumed to be dual frequency (13.5 and 6 GHz) designed to correct out the ionospheric error. The altimeter-carrying satellite will include a nadir pointing near coincidentbeam dual-frequency microwave radiometer for mitigating the wet tropospheric uncertainty. Although there are a number of caveats, the combined uncertainty in the height correction due to the atmosphere for the suggested system should be nominally 3 cm rms compared to at least 6 cm associated with the Seasat-A mission. Improvements in height resolution of the kind referred to here are vital for future satellite missions designed to monitor ocean currents (e.g., TOPEX).

Observation of a strong surface radar duct using helicopter acquired fine‐scale radio refractivity measurements

A very strong surface duct was observed near San Nicolas Island, California, using a unique helicopter-based data acquisition system developed for making fine-scale measurements of radio refractivity in the lower marine troposphere. Such fine-scale measurements are used in a computer model (TEMPER) for predicting microwave propagation in the first 400 m above the ocean surface. The helicopter system makes measurements of atmospheric temperature, pressure, relative humidity, and radar altitude. These measurements are acquired by an on-board computer, which derives and displays real-time plots of modified refractivity versus altitude. Data is stored on floppy disks for later use in the TEMPER (Tropospheric Electromagnetic Parabolic Equation Routine) computer model for microwave propagation prediction. The helicopter measurements are presented and compared with TEMPER computer model microwave propagation predictions using this helicopter data and a standard atmosphere profile.

Rain Measurement Results Derved from a Two-Polarzation Frequency-Diversity S-band Radar at Wallops Island, Virginia

A dual-polarization radar located at the NASA Wallops Flight Facility, Wallops Island, Virginia is described. This radar operates with a slow polarization switch having a cycle time of 0.7 s and also incorporates a frequency diversity technique to achieve independent sampling over short intervals of time. Rain-rate measurements derived from the dual-polarization radar and low-and high-resolution rain gauges located at a remote site are compared. Average percent differences in rainfall of less than 5 and 16 percent were demonstrated when comparing the dual-polarization radar measurement with the low-and high-resolution rain gauges, respectively. Excellent correlation of the rain rates was in evidence during one rain day. All rain measurement cases examined were limited to only light rain rates (less than 7 mm/h).

A High-Power, Dual-Frequency Monostatic Acoustic Sounder for Studying the Atmospheric Boundary Layer

Abstract Microwave propagation conditions in the lower marine troposphere are evaluated using gradients of radio refractivity profiles. An inexpensive, weather-resistant system for Continuous monitoring of radio refractivity conditions in the lower marine troposphere would be useful for deciding when more detailed measurements should be made. Radio refractivity is largely dependent on vertical profiles of water vapor pressure. A high-power, dual-frequency, monostatic acoustic sounder was constructed to investigate the possibility of measuring water vapor pressure profiles in the marine boundary layer by acoustic means. These water vapor pressure profiles may be combined with surface measurements of atmospheric temperature and pressure to obtain estimated radio refractivity profiles. A fundamental assumption for this technique is that the pair of frequencies used should observe the same atmospheric backscatter. That is, the scattering coefficients of the two frequencies should remain a constant ratio. Meas...