Geostationary Interferometric Infrared Sounder (GIIRS)

An infrared hyper-spectral vertical sounder, also the first space-borne interferometer that flies in geostationary orbit to take measurements of three dimensional atmospheric structure from interference of split light beams. Technically featured by a 32×4 sensor array plane, a Michelson interferometer working over different infrared bands for large-area, continuous, fast, and accurate vertical air soundings of temperature and humidity.

Fig. GIIRS of FY-4.

Primary instrument details:

Physical structure Michelson interferometer
Weight 315 kg
Size 1353.5mm(length)×2179.9mm(width)×1549mm(height)
Working bands 700-1130cm-1 (8.85-14.29μm)
1650-2250cm-1 (4.44-6.06μm)
Spectral resolution 0.625cm-1 (actual measurement)
Spectral channels 1650 (actual measurement)
Spatial resolution 16km
Temporal resolution 768km×960km (30min.)
4480km×5000km (60min.)
Radiation calibration accuracy 1.5K
Spectral calibration accuracy 10ppm
Fig. GIIRS scan mode.
Fig. Example of GIIRS scan range. (Example position at 105°E)
Tab. Parameters of FY-4 GIIRS.
FY-4A (R&D) FY-4B (Operational)
Spectral Parameters(Normal mode) Range(cm-1) Resolution Channels Range(cm-1) Resolution Channels
LWIR 700~1130 0.8 538 LWIR 700~1130 0.625 688
S/MIR 1650~2250 1.6 375 S/MIR 1650~2250 1.2 500
VIS 0.55-0.75μm 1 VIS 0.55-0.75μm 1
Spatial Resolution LWIR/S/MIR 16km SSP LWIR/S/MIR 8km SSP
VIS 2km SSP
Operational Mode China area 5000 × 5000 km2 China area 5000 × 5000 km2
Mesoscale area 1000 × 1000 km2 Mesoscale area 1000 × 1000 km2
Temporal Resolution China area <1 hr China area <1 hr
Mesoscale area <½ hr Mesoscale area <½ hr
Sensitivity (mW/m2sr cm-1) LWIR 0.5~1.1 LWIR 0.3
S/MIR 0.1~0.14 S/MIR 0.06
VIS S/N>200(ρ=100%) VIS S/N>200(ρ=100%)
Calibration accuracy (radiation) 1.5k (3σ) 1.0k (3σ)
Calibration accuracy (spectrum) 10 ppm (3σ) 5 ppm (3σ)
Quantization Bits 13 13