Progress in Infrared Sounding Technique
0f Atmospheric Temperature Profile
Mochang Wang , Zhaoxian Zhang
Shanghai Institute of Technical Physics, Chinese Academy of Sciences,
420 Zhong Shan Bei Yi Road, Shanghai 200083, China
Introduction
In the 15 um and 4.3 um absorption bands of carbon dioxide some channels are taken.
The peak values of its weighting functions do not overlap each other from the ground to high
levels of the atmosphere. Each channel contains information of atmospheric temperature for a
certain height range. By means of more complicated calculation measurements from a space-borne
remote sounding instrument can be retrieved to atmospheric temperature profiles. That is
the basic principle of remote sounding of the atmospheric temperature profile.
Infrared spectrometers have been loaded in different meteorological satellites to conduct
mainly three-dimensional remote sounding of atmospheric temperature profile and moisture in
the globe. That is an indispensable instrument and of very important significance for
improvement of numerical as well as middle- and long-term weather forecasting. Since 1980
three versions of IR spectrometer for remote sounding of atmospheric temperature profile have
been developed to accumulate experiences and to make own contributions for the meteorological
remote sensing of our country.
Atmospheric Sounding Infrared Spectroradiometer, version 1 (Experimental model)
In 1980 – 1984, the experimental model of Atmospheric Sounding Infrared
Spectroradiometer, version 1, (ASIS-1) was developed. Its main characteristics is shown in
Tab.1 and its optical schematic diagram is shown in Fig.1.
In its design the scheme comprises a single optical path, nine channels and ten filters, as
well as a pyroelectrical detector. The very difficult key technique of narrow band filter was
resolved during the development. Its main performance met the international advanced level.
The deuterized LaTGS pyroelectrical detector especially developed for ASIS-1 has a Curie-point
temperature of 62° C and, therefore, has good temperature stability at room-temperature.
Tab.1 Characteristics of ASIS-1
experimental model
| field of view | 2.143° |
| stepping angle | 2.7° |
| earth scan angle | +41.85°/-41.85° |
| measurement rate | 2 times/sec |
| measurement number per line | 32 |
| channel number | 9 |
| detector | DLaTGS |
| detectivity of detector assembly | 7.5x109cm Hz1/2W-1 |
| inner blackbody | 285 K, 4 K cold space |
| retrace time | 0.3 sec |
calibration time: inner blackbody
cold space
electrical calibration | 8 sec
8 sec
5 sec |
| quantizing code | 8 |
| number of digital telemetering data | 18 |
| power consumption | ~20 W ( dependent on environment and operation wise) |
| weight ( optical head ) | 16 kg |
| volume ( optical head ) | 600 x 200 x 175 mm3 |
Fig.1 Optical schematic diagram of ASIS-1 experimental model
For ASIS-1 a field optical systemb especially developed for ASIS-1 has a Curie-point
temperature of 62° C and, therefore, has good temperature stability at room-temperature. For
ASIS-1 a field optical system composed of lens and light pipe are used for the first time, whose
design and machining problems were resolved. It has advantages such as high optical efficiency
and fine homogeneity at image surface. ASIS-1 is noted for strict temperature control of its
chopper, filters and TGS detector at a temperature of 35° +/- 0.05° C as a reference of isothermal
cavity. This technique is very difficult.
ASIS-1 was calibrated in a KM-1 thermal vacuum container. The result indicated that
its characteristics corresponds to the similar Vertical Temperature Profile Radiometer (VTPR) on
the meteorological satellite, NOAA, of the United States.
Atmospheric Sounding Infrared Spectroradiometer, version 2 (Experimental model)
In 1986-1991 the experimental model of Atmospheric Sounding Infrared
Spectroradiometer (ASIS-2) was developed, whose main performance corresponds to HIRS-2 on
the third generation operational meteorological satellite of the United States, TIROS-N. But
important improvements were made in the design of system so as to be able to increase long
wave, short wave, near infrared and visible channels.
This instrument was developed after the demands provided by Chinese Meteorological
Bureau. The performances of the 20 channels are shown in Tab.2. By means of a filter wheel
rotating with a rate of 10 cycles / sec the long wave and short wave ranges are separated in 12
and 7 channels, respectively. A PC-HgCdTe detector and an InSb detector were mounted on
field optical systems with light pipes and transform radiant signals to electrical signals. The
visible wave range is received by a Si detector.
A control method using mainly a microprocessor was taken, so that the damping time of
the scan mirror was reduced from 35 ms to 15 ms relative to the control in HIRS-2 using a
stepping motor, a torque motor and a tachometer. The reduction of the damping time
corresponds to increase two LWIR channels and a visible channel and, then, is of important
significance for the measurement time of only 100 ms.
