Engineering topics

Rowlett, J. R.

Publications and source records attributed to Rowlett, J. R..

4 records

NASA NTRS1981

Lidar observation of the mesospheric sodium layer over Urbana, Illinois

Atmospheric sodium has been observed over Urbana (40 deg 10 min N, 88 deg 10 min W) using a monostatic lidar tuned to 589.0 nm. The photocount data are processed using ditital smoothing filters to obtain continuous estimates of the sodium density versus altitude. The filter cutoff frequency is related to the height resolution and accuracy of the estimated profile. Wavelike structures in the sodium layer have been observed with typical wavelengths of 3-15 km and phase velocities of 1-3 m/s. The layer is characterized by a sharp falloff on the bottomside and often an undulatory motion of the bottomside of the layer accompanies the wave motion. The topside gradient of the layer is frequently observed to decrease through the night.

Richter, E. S.↗

NASA NTRS1978

Ray tracing evaluation of a technique for correcting the refraction errors in satellite tracking data

Errors may be introduced in satellite laser ranging data by atmospheric refractivity. Ray tracing data have indicated that horizontal refractivity gradients may introduce nearly 3-cm rms error when satellites are near 10-degree elevation. A correction formula to compensate for the horizontal gradients has been developed. Its accuracy is evaluated by comparing it to refractivity profiles. It is found that if both spherical and gradient correction formulas are employed in conjunction with meteorological measurements, a range resolution of one cm or less is feasible for satellite elevation angles above 10 degrees.

Gardner, C. S.↗

NASA NTRS1978

Lidar observations of wave-like structure in the atmospheric sodium layer

The University of Illinois (Urbana) lidar system has been developed to study the atmospheric sodium layer near 90 km altitude through the mechanism of resonance scattering. The photocount data are processed using digital smoothing filters to obtain continuous estimates of the sodium density versus altitude. The filter cutoff frequency is related to the height resolution and accuracy of the estimated profile. Lidar photocount data processed using this filtering technique show wave-like structures in the sodium layer which move downward with time. The waves have typical wavelengths of 3-15 km and phase velocities of less than 1 m/sec. The movement of these structures seems to be independent of the motion of the bottomside of the layer, which also has been observed to move up or down by as much as 2 km over a period of a few hours.

Rowlett, J. R.↗

NASA NTRS1976

Atmospheric refraction errors in laser ranging systems

The effects of horizontal refractivity gradients on the accuracy of laser ranging systems were investigated by ray tracing through three dimensional refractivity profiles. The profiles were generated by performing a multiple regression on measurements from seven or eight radiosondes, using a refractivity model which provided for both linear and quadratic variations in the horizontal direction. The range correction due to horizontal gradients was found to be an approximately sinusoidal function of azimuth having a minimum near 0 deg azimuth and a maximum near 180 deg azimuth. The peak to peak variation was approximately 5 centimeters at 10 deg elevation and decreased to less than 1 millimeter at 80 deg elevation.

Gardner, C. S.↗