Julie Franklin Kafkalidis

TIMED Doppler interferometer (TIDI)

The TIMED Doppler Interferometer (TIDI) is a Fabry-Perot interferometer designed to measure winds, temperatures, and constituents in the mesosphere and thermosphere (60 - 300 km) region of the atmosphere as part of the TIMED mission. TIDI is a limb viewer and observes emissions from OI 557.7 nm, OI 630.0 nm, OII 732.0 nm, O2(0-0), O2(0-1), Na D, OI 844.6 nm, and OH in the spectral region 550 - 900 nm. Wind measurement accuracies will approach 3 ms-1 in the mesosphere and 15 ms-1 in the thermosphere. The TIDI instrument has several novel features that allow high measurement accuracies in a modest-sized instrument. These include: an optical system that simultaneously feeds the views from four scanning telescopes which are pointed at plus or minus 45 degrees and plus or minus 135 degrees to the spacecraft velocity vector into a high-resolution interferometer, the first spaceflight application of the circle-to-line imaging optic (CLIO), and a high quantum efficiency, low noise CCD.

Operational performance of the TIMED Doppler Interferometer (TIDI)

The TIMED Doppler Interferometer (TIDI) is a Fabry-Perot interferometer designed to measure winds in the mesosphere and thermosphere (60-180 km) as part of the TIMED mission. TIDI is a limb viewer and observes emissions from OI 557.7 nm and rotational lines in the O2(0-0) Atmospheric band. Wind measurement accuracies approach 3 ms-1 in the mesosphere and 15 ms-1 in the thermosphere. The TIDI instrument’s performance during the first year and a half of operation is discussed in this paper. Many subsystems are working as designed. The thermal control system is holding the instrument temperatures at their desired set-points. The CCD detector is working as expected with no changes observed in the gain, bias or read noise. The instrument suffers from a light leak that causes the background to be elevated and increases the uncertainty in the wind measurement. Nothing can be done to eliminate this problem but modeling of the background has eliminated any systematic effect. Water outgassing from the spacecraft or instrument has deposited as ice on some part of the optics and reduced the instrument’s sensitivity. This problem has been reduced by two spacecraft rolls which pointed the TIDI radiator to view more of the earth causing the optics to warm up and sublimate much of the ice.

Mid‐latitude temperatures at 87 km: Results from multi‐instrument Fourier analysis

Using a novel Fourier fitting method we com- bine two years of mid-latitude temperature measurements at 87 km from the High Resolution Doppler Imager, the Colorado State University lidar, and the Peach Mountain Interferometer. After accounting for calibration bias, sig- nificant local-time variations on the order of 10 K were ob- served. Stationary planetary waves with amplitudes up to 10 K were observed during winter, with weaker wave ampli- tudes occurring during other seasons. Because of calibration biases among these instruments, we could estimate the an- nual mean temperature to no better than 193.5 4- 8.5 K. (1991) and recent work by Leblanc et ed. (1999). We present a methodology for making statistical estimates of mid-latitude temperature fields using a combination of satel- lite and ground-based data. Results at a height of 87 km are presented here to illustrate the method and its potential future use with larger multi-instrument data sets. Figure la shows the combined longitudinal and tempo- ral sampling pattern of the temperature field between 41 o 4. 1 o N at 87 km over a two-year period from the High Resolution Doppler Interferometer (HRDI) (Ortland et at.,

High-resolution Doppler imager: instrument performance from late 1991 to mid-1999

The High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite has been providing measurements of the wind field in the stratosphere, mesosphere, and lower thermosphere since November 1991. Mesospheric temperatures, ozone and O(1D) densities, and stratospheric aerosol extinctions coefficients, are also retrieved. The instrument characteristics have been carefully monitored by frequent calibrations during the nearly eight years of operation. The instrument sensitivity showed a significant decrease (close to 50% in some cases) during the first seven and a half years of operation which was caused by the piezoelectric-controlled etalons slowly drifting from a parallel state. A recalibration of the etalons in late 1998 resulted in close to a complete recovery of the instrument sensitivity. The loss of sensitivity was linear with time, with discrete changes occurring at times. Careful modeling of the data permits a determination of the sensitivity as a function of time, allowing the data to be corrected for this systematic effect.

High-Resolution Doppler Imager: instrument performance in orbit since late 1991

The high resolution doppler imager (HRDI) on the upper atmosphere research satellite has been providing measurements of the wind field in the stratosphere, mesosphere and lower thermosphere since November 1991. Mesospheric temperatures, ozone and O(1D), as well as stratospheric aerosol extinctions, are also recovered. The instrument characteristics have been carefully monitored during the nearly five years of operation. The instrument thermal and long-term drifts can be removed from the data, and wind biases are less than about 2 m/s. The interferometer sensitivity has varied by about 3 percent, most likely due to changes in the parallelism of one of the etalons. There is not indication that either the radiator or thermal blankets have shown any significant degradation. Recently, the azimuth slew rate of the telescope has displayed some variation, which may indicate an increase of bearing friction.