FY-4A Instruments

Advanced Geostationary Radiation Imager (AGRI)

A multiple channel radiation imager, one of the primary instruments aboard FY-4A. Technically featured by precisely designed two-mirror structure, capable of accurate and flexible sensing in two dimensions, and minute-level fast sector scanning. Frequent earth imaging over 14 bands with off-axis three reflections of primary optic system. On-board black body available for IR calibrations at very short time intervals.

Fig. AGRI of FY-4.

Primary instrument details:

Weight	306 kg
Number of channel	14, including 6 visible/near infrared bands, 2 mid-wave infrared bands, 2 water-vapor bands and 4 long-wave infrared bands
Spatial resolution	0.5~1 km (VIS/near IR), 2~4 km (IR)
Time for full-disc scanning	15 min
Time for sector scanning	1 min (1000km×1000km)
Sensitivity	S/N>3 @ 1% (reflection bands) NE∆T: 0.2K @ 300K (IR bands)

Demo of FY-2 VISSR scan mode.	Demo of FY-4 AGRI scan mode.

Range of regional scan: 3°~55°N, 60°~137°E.

Fig. Example of AGRI scan range.

Tab. Example products by AGRI channels.


0.45～0.49μm	0.55～0.75μm	0.75～0.90μm	1.36～1.39μm	1.58～1.64μm	2.1～2.35μm	3.5～4.0μm (2km)

3.5～4.0μm (4km)	5.8～6.7μm	6.9～7.3μm	8.0～9.0μm	10.3～11.3μm	11.5～12.5μm	13.2～13.8μm

Tab. Comparison of FY-4 AGRI with FY-2 VISSR.

Channel	FY-2F/G/H VISSR			FY-4A AGRI			Main Application
Channel	Band(μm)	Spatial Resolution(km)	Sensitivity	Band(μm)	Spatial Resolution(km)	Sensitivity	Main Application
Visible & Near-Infrared	N/A	N/A	N/A	0.45～0.49	1	S/N≥90(ρ=100%)	Aerosol
	0.55～0.75	1.25	2.3@ρ=1%	0.55～0.75	0.5～1	S/N≥200(ρ=100%)	Fog, cloud
	N/A	N/A	N/A	0.75～0.90	1	S/N≥5(ρ=1%)@0.5Km	Vegetation
Short-wave Infrared	N/A	N/A	N/A	1.36～1.39	2	S/N≥200(ρ=100%)	Cirrus
	N/A	N/A	N/A	1.58～1.64	2		Cloud, snow
	N/A	N/A	N/A	2.1～2.35	2～4		Cirrus, aerosol
Mid-wave Infrared	N/A	N/A	N/A	3.5～4.0(High)	2	NEΔT≤0.7K(300K)	Fire
Mid-wave Infrared	3.5～4.0	5	0.22K@300K	3.5～4.0(Low)	4	NEΔT≤0.2K(300K)	Land surface
Water vapor	N/A	N/A	N/A	5.8～6.7	4	NEΔT≤0.3K(260K)	Water vapor
Water vapor	6.3～7.6	5	0.30K@260K	6.9～7.3	4	NEΔT≤0.3K(260K)	Water vapor
Long-wave Infrared	N/A	N/A	N/A	8.0～9.0	4	NEΔT≤0.2K(300K)	Water vapor, cloud
	10.3～11.3	5	0.12K@300K	10.3～11.3	4	NEΔT≤0.2K(300K)	Surface temperature
	11.5～12.5	5	0.16K@300K	11.5～12.5	4	NEΔT≤0.2K(300K)	Surface temperature
	N/A	N/A	N/A	13.2～13.8	4	NEΔT≤0.5K(300K)	Cloud thickness

Fig. AGRI transmittance over wavelength.

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

Range of regional scan: 3~55°N, 60~137°E.

Fig. Example of GIIRS scan range.

IR bands:

Tab. Parameters of FY-4 GIIRS.

Band	Range	Sensitivity	Calibration accuracy
LWIR	700 ~ 1130 cm^-1	0.5 ~ 1.1 mW/(m²sr cm^-2)	1 K
MWIR	1650 ~ 2250 cm^-1	0.1 ~ 0.14 mW/(m²sr cm^-2)	1 K

VIS band:

○ SNR: S/N ≥ 200 (ρ=100%)

○ Calibration accuracy: 10 ppm

One of the first two lightning mappers for geostationary meteorological satellite in the world, and the Chinese first ever made instrument such as this. Technically featured by planar CCD array and optic imaging sector, to keep track of thunderstorm development by detecting and mapping the lightning events occurring in a cloud, cloud-cloud, or cloud-ground within the observation area. For service to aviation, railway, power supply company, as well as strong convective weather monitoring. LMI/FY-4 looks at China area in spring-autumn seasons, and at Indian ocean and west Australia the rest of a year.

Fig. LMI of FY-4

Tab. Parameters of FY-4 LMI.

Spatial resolution	about 6 km at SSP
Wave-length at center	777.4nm
Band-width	1nm±0.1nm
Detection efficiency	>90%
False-alarm ratio	<10%
Dynamic range	>100
SNR	>6
Frequency of frames	2ms (500 frames per sec.)
Quantization	12 bits
Measurement Error	10%

LMI observes lightning in the Northern Hemisphere from Vernal Equinox to Autumnal Equinox, and in the Southern Hemisphere from Autumnal Equinox to next year's Vernal Equinox.


Fig. LMI observation range in the Northern Hemisphere.	Fig. LMI observation range in the Southern Hemisphere.

Space Environment Package (SEP)

A suite that contains energetic particle detectors, magnetometer, and space weather impact detectors, among which, the energetic particle detectors measure high energy protons (0.4～4MeV) and high energy electrons (1～165MeV, and >165MeV) with two probes. Particle flux detection is performed in multiple directions with a number of probes mounted toward different orientation on the three-axis stabilized spacecraft. The space weather impact detectors measure radiation dosage, electrification at the surface and deep inside the spacecraft. It’s the first time China put space weather impact and space environment detectors on the same geostationary platform.

SEP consists the following instruments:

HEPD: High Energy Particle Detector
RADD: Radiation Detector
CPD: Charging Pressure Depth
FGM: Field Geo Magnetic

Fig. SEP of FY-4.