RIS Science Team Meeting Report
(March 15, 1997)
RIS Science Team Meeting was held on March 13, 1997 in the 2nd ADEOS workshop (March 10-14, 1997, Yokohama).
Sammary of the RIS program report (presented in the plenary session of the workshop on Mar. 11, 1997)
1. The optical characteristics of RIS was tested in the initial checkout period. It was comfirmed that the return detected by the ground station was close to the theory for both visible and infrared lasers.
2. Active tracking using the image of RIS lit by visible laser was established. Tracking accuracy of approximately 30 microradians is obtained.
3. Laser ranging to RIS was established. Laser ranging support is obtained from 14 satellite laser ranging stations. The orbital prediction using the laser ranging data is used in the RIS experiment.
4. The first spectrum with earth-satellite-earth laser long-path absorption method was obtained using the TEA CO2 lasers. Absorption spectrum of ozone was recorded with the method using the Doppler shift of reflected beam which is caused by the satellite movement. The shape of the measured spectrum agreed with the theory. However, the error in the measured spectrum was larger than expected.
5. Column content of ozone was obtained from the spectrum.
6. The error in the measurement was studied. It was found that the intensity of the infrared signals was sufficient, but the correlation between the return pulses from the two lasers was low. The probable cause of the error was a slight difference between the beam patterns of the two TEA CO2 lasers, which caused different beam pattern at the satellite when propagated through the turbulent atmosphere. Based on the study, the transmitter optics was improved using a spatial filter which consists of lenses and a pinhole.
7. The experiment on spectrum measurement is continued with the improved transmitter.
Summary of the RIS Science Team Meeting (March 13, 97)
A) Spectroscopic Measurement
1. Problem with errors in the spectrum measurement was discussed.
- Error was improved by the use of the spatial filter.
- Recent test measurement shows that a single shot signal-to-noise ratio (SNR) of 10 is obtained.
- From the data analysis point of view, a single shot SNR of greater than 10 is acceptable for retrieving profile of ozone.
- Further improvement of the tracking error is required.
2. Measurement Plan
- Measurement of ozone will be continued. After the quality of the data with the current transmitter system is validated, measurement of other species will be started.
B) Satellite Laser Raanging (SLR) to RIS
1. Orbital Prediction
- More than 20 SLR stations were registersd for ADEOS/RIS laser tracking. 6-7 stations among them have made regular operation.
- Orbital prediction by NASDA/TCC using the SLR data has been working successfully.
2. Presice Orbit Determination
- For the research on precise determination of ADEOS orbit, more SLR data is required. One moth (per half a year) tracking campaign is recommended.
3. Two Color Ranging Experiment
- Two color ranging experiment at NASA/GSFC was reported by Dr. J. Degnan. Clean single pulse returns at 532 nm and 355 nm have been received.
The single element feature of RIS was proved to be useful for precise laser ranging.