The FY-1C Meteorological Satellite and Its Remote Sensor
Remote Sensor
The 10-channel scanning radiometer is the main instrument of the FY-1C satellite. It is shown
in Fig.2 and its optical configuration is shown in Fig.3. By means of the rotation of a 45° mirror of
the scanning radiometer and the motion of the satellite round the earth, the two-dimensional scene of
the earth is observed.
The rotation rate of the scanning mirror is 360 rpm. The aperture of the optical system is 200
mm. The bands for 10 detecting channels are limited by the filters located in front of detectors. The
detectors for visible and near infrared channels are Si and those for short wavelength infrared
channels are PV-type HgCdTe operating at room temperature. Three thermal infrared detectors are
all PC-type HgCdTe operating at 105 K, cooled by a radiant cooler.
The 10-channel scanning radiometer was developed on the basis of the 5-channel scanning
radiometers for FY-1A and FY-1B. Its 10 channels are listed in table 1. (Compared with the
AVHRR on NOAA satellite, three visible channels and one near infrared channel are added, which
are used for the detection of ocean chlorophyll, ocean suspended sediment, and water vapor content
in atmosphere, respectively.)
Fig.2 The scanning radiometer.
Fig.3 The optical configuration of the scanning radiometer.
Among them, 0.58-0.68
mm band is used to take visible cloud images. The 0.84-0.89
mm band
has a high atmosphere transmittance and it is used for the atmospheric radiation correction of visible
and near infrared channels and is also used to monitor vegetation index together with the 0.58-0.68
band. Channel 3 is sensitive to high temperature objects, so it is used to monitor forest and grassland
fire. The thermal infrared split window bands of 10.3-11.3
mm and 11.5-12.5
mm are used to
measure ocean surface and land surface temperatures. In 1.58-1.64
mm band, the reflectance is
reduced when the water content in soil is increased. So this band is used to detect the moisture of soil.
The reflectance of snow is reduced as the wavelength is increased. In 1.58-1.64
mm band, the
reflectance of snow is less than 25%. So the images of this band together with the visible cloud
images are used to discriminate cloud and snow. Channels 7, 8 and 9 are used to monitor the ocean
chlorophyll and suspended sediment. The transmittance of channel 10 is influenced by water vapor,
so this channel and channel 2 can be used to monitor the water vapor content in atmosphere.
Table 1. The detection bands of
10-channel scanning radiometer
| Serial number | Detection band (mm) | Objects | FY-1A,B 5-channel scanning radiometer | NOAA AVHRR |
| 1 | 0.58-0.68 | Cloud, vegetation | Ö | Ö |
| 2 | 0.84-0.89 | Vegetation, atmospheric correction | 0.725-1.1mm | 0.725-1.1 mm |
| 3 | 3.55-3.93 | Fire and night temperature | | Ö |
| 4 | 10.3-11.3 | Ocean surface and land surface temperature | 10.5-12.5 mm | Ö |
| 5 | 11.5-12.5 | Ocean surface and land surface temperature | | Ö |
| 6 | 1.58-1.64 | Crop water content and soil moisture | | Ö |
| 7 | 0.43-0.48 | Ocean water color | | |
| 8 | 0.48-0.53 | Ocean water color | Ö | |
| 9 | 0.53-0.58 | Ocean water color | Ö | |
| 10 | 0.900-0.965 | Vapor content | | |
Table 2 lists the main specifications of the 10-channel scanning radiometer. The ten detecting
channels all have a spatial resolution of 1.26mr and an effective scanning observing angle of ±
55.4° on both sides of the nadir, corresponding to the arc length of 3100 km on earth surface. Its
global coverage period is 24 hr. The user's test from June to July shows that the sensitivity of the
visible and near-infrared channels are better than 3.5×10 -4 , the NED rof the short wavelength IR
channel is 1.1×10 -3 , the NEDT of three thermal IR channels is less than 0.27 K . Because a
reference blackbody is mounted and the cold space is used as a zero radiation reference, the radiation
calibration reaches an accuracy of 1.0 K.
