The HY-2 satellite and its preliminary assessment

Figures & data

Table 1. Main parameters of the HY-2 radar altimeter.

Frequency	13.58 GHz, 5.25 GHz
Pulse-limited footprint	<2 km
Frequency bandwidth	320 MHz
Pulse Repetition Frequency	2 KHz

Table 2. Main parameters of the HY-2 scatterometer.

Frequency	Ku band (13.256 GHz)
Transmit power	120 W
Pulse width	1.5 ms
Swath	1350 km for inner beam; 1750 km for outer beam
Polarization	HH for inner beam; VV for outer beam
Look angle	34.8° for inner beam; 40.8° for outer beam
Incidence angle	41° for inner beam; 48° for outer beam
Scanning mode	Conically scanning
Antenna rotation rate	95°/s for low rate; 105°/s for high rate
σ0 measurement accuracy	0.5 dB
σ 0 measurement range	−40 dB to +20 dB
Wind cell resolution	25 km
Wind speed accuracy	<2 m/s or <10%
Wind direction accuracy	<20° RMS
Mission lifetime	3 years

Table 3. Main parameters of the HY-2 RM.

Frequency (GHz)	6.6	10.7	18.7	23.8	37.0
Polarization	V H	V H	V H	V	V H
Scan width (km)	1600
Footprint size (km)	100	70	40	35	25
Sensitivity (K)	<0.5	<0.5	<0.5	<0.5	<0.8
Dynamic range (K)	3−350
Calibration precision (K)	1 (180−320)

Table 4. Main characteristics of the HY-2 satellite and its orbit.

Orbit type	Sun-synchronous
Equator crossing local time	6:00 AM
Altitude	970 km
Inclination	99.3°
Period	104.45 min
Attitude control	Three axes stabilized
Downlink frequency	X-band
TT&C link	S-band
Designed lifetime	Three years
Launch vehicle	LM-4B
Manufacturer	CAST
Launch site	Taiyuan

Table 5. HY-2 dynamic model.

Model	HY-2
Earth geo-potential	EIGEN_GL04 120×120 order
N-body	DE405 (all planets, sun and moon)
Solid tide	IERS2003
Ocean tide	CSR4.0
Relativity	General-relativistic effect
Atmosphere drag	DTM94
Solar radiation pressure	Surface integration model
Empirical dynamic mode	RTN periodic empirical perturbation
Earth rotation parameters	IERS Bulletin B
Orbit integration	5 s integration step, 11 order Adams

Table 6. HY-2 estimation parameters.

Estimation parameters	Specification
HY-2 initial position	1000
HY-2 initial speed	2 m/s
On-board GPS receiver clock bias: white noise	9000 m
Ambiguity	10,000 cycle
HY-2 atmosphere drag coefficients	Estimate one time/6 h
HY-2 ACR empirical dynamics	Estimate one periodic term/6 min

Figure 1.  Comparison of the sea surface height from the HY-2 and Jason-2 altimeters. (a) HY-2 altimeter SSH; (b) Jason-2 altimeter SSH.

Figure 2.  Comparison of the SWH from HY-2 and Jason-2 altimeters. (a) HY-2 altimeter SWH; (b) Jason-2 altimeter SWH.

Figure 3.  Comparison of the WS from HY-2 and Jason-2 altimeters. (a) HY-2 altimeter WS; (b) Jason-2 altimeter WS.

Figure 4.  (a) σ ₀ scatter plot of the inner beam for an ascending pass; (b) σ ₀ scatter plot of the inner beam for a descending pass; (c) σ ₀ scatter plot of the outer beam for an ascending pass; (d) σ ₀ scatter plot of the outer beam for a descending pass.

Table 7. Mean value and standard deviation of σ₀ for rain forest.

	Inner beam	Inner beam	Outer beam	Outer beam
	Ascending pass	Descending pass	Ascending pass	Descending pass
Mean (dB)	−5.88595	−5.68927	−5.78114	−5.60911
Std (dB)	0.422048	0.392694	0.401467	0.309345

Figure 5.  (a) Wind field retrieved by the HY-2 scatterometer; (b) NCEP wind field.

Figure 6.  Synoptic cyclone and front structure captured by the HY-2 scatterometer.

Table 8. Comparison of HY-2 RM and NCEP re-analysis products.

Oceanic geophysical quantity	SST (°C)	SSW (M/S)	WV (Kg/m^2)	CLW (Kg/m^2)
RMS	2.0872	2.1990	2.1948	0.0498

Figure 7.  (a) SST retrieved by the HY-2 RM; (b) wind speed retrieved by the HY-2 RM.

Figure 8.  RMS of radial difference with CNES.