6. Results - Spectrum Measurement with the RIS
Atmospheric spectrum was obtained by means of the Doppler shift method with the TEA CO2 lasers. The Doppler shift can be expressed by Df = (2vf/c) cos q, where v is velocity of satellite, f is frequency of the laser, and q is elevation angle to the satellite. Because the speed of the ADEOS is 7 km/s, and the spectral range covered by the Doppler shift is 0-1.3 GHz (0-0.04 cm-1) at 10ƒÊm. Figure 6-1 shows the first spectrum measured with the RIS. The two TEA CO2 lasers are tuned to 10R(24) line of 13CO2 and 9P(24) line of 12CO2, respectively. The vertical axis indicates logarithm of the ratio of the signal intensity for primary laser to that for reference laser. The horizontal axis indicates shot number. The wavelength of the return light changes with the shot number because of the change in the Doppler shift. The dip seen in Fig. 6-1 is due to the absorption of ozone that 9P(24) line of 12CO2 received. The lower panel in Fig. 6-1 shows a simulated spectrum generated with the HITRAN absorption line database and the US standard ozone profile. The measured spectrum agreed with the simulated spectrum, though the error in the measurement was larger than expected.
Fig. 6-1 The first spectrum measured with the RIS (upper),
and simulated spectrum (lower).
To validate the ozone measurement with the RIS, a simultaneous ozone measurement with a laser heterodyne spectrometer was carried out in cooperation with Tohoku University. Because the laser heterodyne spectrometer used a different absorption line of ozone in the 10 micron region, we compared the spectrum measured by the RIS with the spectrum calculated from the ozone profile measured with the laser heterodyne spectrometer. The shape and intensity of the measured spectrum agreed well with the calculated spectrum.
The error in the measurement was studied. It was found that the probable cause of the error was a slight difference between the beam patterns of the two TEA CO2 lasers. Based on the analysis, the transmitter optics was improved by adding a spatial filter consisting of a pair of lenses, a pinhole. As the result, error in the measurement was improved approximately 5 times. A single shot signal-to-noise ratio of 10 in the ratio of the received power was achieved.
7. Results - Orbital determination of ADEOS by laser ranging to the RIS
8. Future perspective
9. Publications
1. Outline of the RIS Experiment
2. The RIS on the ADEOS
3. Ground system for the RIS experiment
4. Results - Active tracking using image of the RIS
5. Results - Optical characteristics of the RIS
Return to RIS home page