Performance Analysis of Microwave Humidity and Temperature Sounder Onboard the FY-3D Satellite From Prelaunch Multiangle Calibration Data in Thermal/Vacuum Test

A newly designed thermal/vacuum (T/V) prelaunch multiangle calibration test is proposed for Microwave Humidity and Temperature Sounder (MWHTS) onboard the Feng Yun 3D satellite. Compared with other existing prelaunch calibration tests designed at fix scan angle, this test is first proposed to analyze the measurements of MWHTS from multiscan angles. A set of comprehensive calibration method is established and used for calibration data processing. The high-quality data preprocessing methods are performed. Essential calibration coefficients such as cold bias, hot bias, and nonlinearity coefficients, and calibration results such as calibration residual error, sensitivity, and calibration accuracy of MWHTS are all obtained and analyzed in MWHTS's six observing positions. The measured sensitivity value of channel 2 is 1.5 K while the measured sensitivities of the others range from 0.18 to 0.57 K. The calibration accuracy of channel 2 is 1.5 K while the calibration accuracies of the others range from 0.32 to 0.7 K. According to the discrepancy of multiangle calibration test results, the radiation leakage and the response lag for special channels are discovered for the first time in T/V test, and the reasons of these two special phenomena are fully analyzed. Moreover, the measurements of the T/V test with fast changing instrument temperatures are analyzed and the applicability of nonlinearity coefficients obtained in T/V test for in-orbit calibration is verified. In conclusion, MWHTS meets the basic design requirements of sensitivity and calibration accuracy, the changing of the MWHTS observing positions does not impact the calibration coefficients and results, and the nonlinearity coefficients obtained in T/V test are valid when instrument temperature experiences some fast changing.

I. Introduction

Feng Yun 3D (FY-3D) is the second operational satellite of China’s second generation polar-orbiting meteorological satellites. It works as an afternoon satellite with Feng Yun 3C (FY-3C), which is the first operational satellite and works as a morning satellite, to achieve constellation observation. Due to the requirement of all-weather observation, the Microwave Humidity and Temperature Sounder (MWHTS) onboard the FY-3C/3D satellite is a significant microwave payload [1]. The FY-3C MWHTS has successfully detected atmospheric temperature, humidity profiles, typhoon, rainfall, and other meteorological disaster information since its initial operating, and the operational capability of FY-3C satellite has been approved for more than four years. The MWHTS onboard FY-3D is identical to the MWHTS onboard FY-3C. The MWHTS contains 15 observing channels at 89, 118.75, 150, and 183.31 GHz [2]. Table I summarizes the requirements of all MWHTS channels. Compared with other similar payloads, such as Microwave Humidity Sounder (MWHS) [2], Advanced Microwave Sounding Unit-B (AMSU-B) [3], Microwave Humidity Sounder (MHS) [4], Humidity Sounder for Brazil (HSB) [5], and Advanced Technology Microwave Sounder (ATMS) [6], [7], the first use of 118.75 GHz observing channels makes MWHTS unique in detecting the temperature of upper troposphere. Fig. 1 shows the schematic of MWHTS. MWHTS consists of three units: antenna and receiver unit, power supply unit, and data processing electronic unit. MWHTS has two separate scan reflectors. One is for channels 1–9 at 89 and 118.75 GHz, the other is for channels 10–15 at 150 and 183.31 GHz. The MWHTS is a cross-track scanning total-power microwave radiometer. Fig. 2 shows the scan mode and geometry of MWHTS. MWHTS’s scan period is 2.667 s, and each scan period contains three scan segments. In the first scan segment, three samples are taken from the hot target for calibration [8]. After that, three samples are taken from the cold target for calibration in the second scan segment. In the last scan segment, 98 pixels are taken from the Earth scenes with MWHTS scan angle ranges uniformly within ±53.35° from the nadir direction symmetrically. The antenna of MWHTS scans at a constant speed within each of the three scan segments, and accelerates between any of the two segments.TABLE I Requirements of ALL MWHTS Channels

Channel	Center Frequency (GHz)	Polarization	Bandwidth (MHz)	Dynamic range (K)	NER (K)	Calibration accuracy (K)	3dB Beam width	Main Beam efficient
1	89.0	QV	1500	3–340	1.0	1.3	2.0°	>92%
2	118.75±0.08	QH	20	3–340	3.6	2.0	2.0°	>92%
3	118.75±0.2	QH	100	3–340	2.0	2.0	2.0°	>92%
4	118.75±0.3	QH	165	3–340	1.6	2.0	2.0°	>92%
5	118.75±0.8	QH	200	3–340	1.6	2.0	2.0°	>92%
6	118.75±1.1	QH	200	3–340	1.6	2.0	2.0°	>92%
7	118.75±2.5	QH	200	3–340	1.6	2.0	2.0°	>92%
8	118.75±3.0	QH	1000	3–340	1.0	2.0	2.0°	>92%
9	118.75±5.0	QH	2000	3–340	1.0	2.0	2.0°	>92%
10	150.0	QV	1500	3–340	1.0	1.3	1.1°	>95%
11	183.31±1	QH	500	3–340	1.0	1.3	1.1°	>95%
12	183.31±1.8	QH	700	3–340	1.0	1.3	1.1°	>95%
13	183.31±3.0	QH	1000	3–340	1.0	1.3	1.1°	>95%
14	183.31±4.5	QH	2000	3–340	1.0	1.3	1.1°	>95%
15	183.31±7	QH	2000	3–340	1.0	1.3	1.1°	>95%

Note: In column 3, QV/QH means quasi V/H polarization

Fig. 1.

Schematic of MWHTS.

Fig. 2.

Scan mode and geometry of MWHTS.