2.3 The FY-1C and FY-1D
China will continue the development of FY-1
series and to launch FY-1C and FY-1D in
the year of 1999 and 2001 respectively. Now
the satellites are developed on the basis of
FY-1A and FY-1B. Besides the efforts to
improve the reliability of the satellites there
are some changes on imaging instruments
and data transmission as follows:
- The channel numbers of the Visible and
Infrared Radiometers are increased to ten
channels, which enables the more powerful
observations to the land and oceans.
- The on board data storage capacity is
increased to 300 minutes (60 minutes on
FY-1A/B). This means that besides the real
time received CHRPT data within the
Beijing, Guangzhou and Urumqi three
ground station acquisition areas, we can
receive global coverage data of four selected
channels with reduced resolution (4 km) for
one time each day (defined as Delayed
Global Picture Transmission, DGPT), as
well as 20 minutes orbit observation data of
ten channels with original resolution at any
region of the world (defined as Delayed
Local Picture Transmission, DLPT).
- The FY-1C and FY-1D High Resolution
Picture Transmission will be also very
similar to NOAA/HRPT, except the data
transmission rate. It is considered that the
system that receives and process
NOAA/HRPT nowadays can receive and
process the FY-1 data with updating as few
as possible. The data transmission rate is
double that of current NOAA/HRPT, i.e.,
the data transmission is 1.3308 Mbps. The
transmission modulation is PSK and bit
format is split phase.
- The design life of FY-1C/D is two years.
- There is no APT in FY-1C and FY-1D.
The instantaneous field of view of the
radiometer is 1.2 mrad and the resolution at
the satellite subpoint is 1.1 km. The scan
rate is still 6 lines/sec and the total pixels of
each scan line are 2048. The channel
features of the main payload on FY-1C and
FY-1D: the ten-channel Visible and Infrared
Radiometers are indicated in table 3.
Table 3. The channel characteristics of radiometers onboard FY-1C and FY-1D
| Channel |
Wavelength(µm) |
Primary Use |
| 1 |
0.58-0.68 |
Daytime cloud, ice and snow, vegetation |
| 2 |
0.84-0.89 |
Daytime cloud, vegetation |
| 3 |
3.55-3.95 |
Heat source, night cloud |
| 4 |
103.-11.3 |
SST, day/night cloud |
| 5 |
11.5-12.5 |
SST, day/night cloud |
| 6 |
1.58-1.64 |
Soil moisture, ice/snow distinguishing |
| 7 |
0.43-0.48 |
Ocean color |
| 8 |
0.48-0.53 |
Ocean color |
| 9 |
0.53-0.58 |
Ocean color |
| 10 |
0.90-0.985 |
Water vapor |
On May 10, 1999, FY-1C was launched
successfully and now the satellite is
operating well. Many new images and
products are produced based on the FY-1C
data. A separated paper will describe the
FY-1C products in more detail.
3. Geostationary meteorological satellite
program of China
3.1 General
China has launch its first geostationary
meteorological satellite FY-2A with the
Long March-3 rocket from the Xi Chang
Satellite Launching Center on 10, June 1997.
The satellite is located in the equator of
105
°E.
FY-2 satellite data is open for international
users, therefore the satellite data can be
shared with other countries. User stations
covered by FY-2 can receive S-VISSR high
resolution digital data and WEFAX low
resolution analog data.
3.2 Specifications of FY-2 satellite and the
radiometer
3.2.1 Functions of the satellite
FY-2 meteorological satellite has the
following functions:
- Obtaining visible, infrared and water
vapor cloud images by a radiometer on
board satellite. Sea surface temperature,
cloud analysis chart, cloud parameters
and wind vector can be derived from
these data.
- Collecting and transmitting observed
data from widely dispersed data
collection platforms.
- Broadcasting S-VISSR data, WEFAX
and S-FAX or processed cloud images
- Monitoring space environmental from
satellite.
Table 4. FY-2 Satellite Specifications
| Dimensions |
Diameter Height |
2.1 m 1.6 m (cylinder ) |
| Mass |
Launch On Station |
1200 kg 520 kg |
| Life span |
Designed |
3 years |
| Orbit |
Geostationary |
located at 105°E |
| Attitude |
Spin-stabilized, Spin rate |
100±1 rpm |
| Launch Vehicle |
Long March-3 |
|
3.2.2 Visible and infrared spin scan
radiometer
The major payload of FY-2 meteorological
satellite is Visible and Infrared Spin Scan
Radiometer (VISSR) . The characteristics of
the instrument are shown in Table 5.
Table 5. Major Characteristics of VISSR
| |
Visible |
Infrared |
Water Vapor |
| Wavelength |
0.5-1.0.5 µm |
10.5-12.5 µm |
6.2-7.6 µm |
| Resolution |
1.25 Km |
5 Km |
5 Km |
| FOV |
35 µrad |
140 µrad |
140 µrad |
| Scan Line |
2500*4 |
2500 |
2500 |
| Decector |
Si-photo-diode |
HgCdTe |
HgCdTe |
| Noise Performance |
S/N=6.5
(albedo=2.5%)
S/N=43
(albedo=95%) |
NEDT=o.5-
0.65k
(300k) |
NEDT=1k
(300K) |
| Quantification Precision |
6 bits |
8 bits |
8 bits |
| Scan step angle |
140 µrad(N-S scanning) |
|
|
| Frame time |
30 minutes |
|
|
The VISSR performs Earth and cloud
observations from space. Visible, infrared
and water vapor images of he Earth and its
clouds are derived from the VISSR. During
a scanning, the optical telescope collects
visible, infrared and water energies from the
Earth and clouds, and then focuses them on
the focal plane with primary and secondary
mirrors. Visible fiber optics and infrared
relay optics system relay energies from the
telescope focal plane to visible, infrared and
water vapor detectors. Si detectors convert
visible light into visible analog signals and
HgCdTe detectors cooled by radiation
coolers convert the Earth’s radiation into
infrared analog signals. The S-VISSR
outputs are fed to a VISSR Digital
Multiplexer (VDM) unit with redundancy.
- Visible Channel (0.55-1.05 µm)
Four Si detectors and redundant sets
simultaneously convert visible light into
four-channel visible analog signals of 1.25
km resolution at the sub-satellite point (SSP)
with one west-east scanning.
- Infrared Channel (10.5-12.5 µm)
High sensitive HgCdTe detectors with
redundancy, which are kept at a temperature
of 100K by the radiation cooler, convert
Earth radiation into infrared analog signals
with 5 km resolution images at SSP
- Water Vapor Channel(6.3-7.6 µm)
Extremely sensitive HgCdTe detectors with
redundancy, which are kept at a temperature
of 100K by the radiation cooler, convert
Earth radiation into infrared analog signals
with 5 km resolution images at SSP
- Imaging
A complete 20
°×20
° scan covering the full
Earth disk can be accomplished every 30
minutes by means of combination of satellite
spin motion (100 rpm from west-east) and
step action of the scan mirror (2500 steps
from north to south). It takes 25 minutes for
taking picture, 2.5 minutes for mirror retrace,
and 2.5 minutes for VISSR stabilization.
