Conference Agenda

The Microwave Radiometer (MWR) flown on Envisat, ERS-1 and ERS-2 provides a nearly uninterrupted time series of microwave observations over a period almost 21 years between 1991 and 2012. This dataset is complementary to other microwave datasets. From 2011, the Atmospheric Correction Microwave Radiometer (ACMR) on HY-2 provides similar measurement.

Firstly, we report on our efforts towards a fully inter-calibrated and validated physical retrieval of TCWV and LWP for MWR. We will address issues related to satellite inter-calibration, homogeneity of the derived time series of brightness temperatures, observation-simulation biases, and provided first results of fully physical retrievals.

Secondly, an outlook on ongoing and planned activities within Dragon-4 will be given and the importance of the results in light of the upcoming Sentinel-3 mission and the HY-2 series will be discussed.

Calibration and validation (Cal&Val) is one of the most important means for assuring satellite payload performance and data quality. It could guarantee the accuracy of the retrieved information, make the remote sensing data consistent and traceable, and maintain the sensor performance during the operational phase. The challenges in the Cal&Val include the lack of consistent remote sensing (RS) product assessment standards, the uncertainties introduced by atmospheric effect, as well as the gaps in non-synchronous measurements between satellite observation and in situ measurements. In this project, great achievement has been done in carrying out cooperative research on the high-frequency optical calibration with the aid of the Radiometric Calibration Network (RadCalNet) activities and permanent targets over Baotou site in China.

(1) Development of automated radiometric calibration system and its operations. On benefit of RadCalNet and the cooperation of the Cal&Val experts from European and Chinese intuitions in the DRAGON programme, the automated surface spectral reflectance measurement system has being developed and installed over four permanent targets with different reflectance in Baotou site, which can automatically and traceably acquire the target characteristics and atmospheric parameters. In consideration of the land surface variety and the adjacent effect, the TOA radiance is simulated with the input of a background reflectance driving the MODTRAN, and the Level 1 BOA reflectance product is generated according to the input files defined by RadCalNet data center.

(2) Automated radiometric calibration demonstration for Chinese and European satellites. The data portal for standard product service has been established under the leadership of ESA, and now is in operation. Since the late last year, ESA have organized test users to calibrate their satellites using the RadCalNet standard products over four demonstrated sites. Among them, the predicted TOA radiance over Baotou site is compared with the observations of Sentinel-2a, ZY-3, GF-1, etc. This is not only important to validate the calibration capability of Baotou site, but also would greatly benefit improving the calibration accuracy of optical sensors, and assuring the data consistency from different sensors.

(3) The uncertainty analysis on the standard radiometric calibration product. The calibration uncertainty over Baotou site include the following aspects: 1) Traceable accuracy and measurement repeatability of the automated measurement system, traced to the primary standard of NPL through the transfer calibrator; 2) Non-uniformity and BRDF effect of the ground standard targets; 3) Measurement errors of typical atmospheric parameters, which are given by AERONET since the sun-photometer Cimel CE-318 in Baotou site has been included in AERONET; 4）Adjacent effect, caused by the point spread function (PSF) of the imaging system and the multiple scattering among surface and atmosphere; 5) Uncertainty aroused by radiative transfer calculation of MODTRAN, which is simulated based on Monte-Carlo theory.

A ground-based MAX-DOAS and a Bruker IFS 125HR have been deployed in Xianghe Station, Northern China, of the Institute of Atmospheric Physics, Chinese Academy of Sciences, and another Bruker IFS 125M has been installed in Xinglong Station. The MAX-DOAS has been running for more than ten years, providing a large number of high quality data of NO₂, SO₂, etc., for deriving their trends, and for validating the satellite products of OMI, GOME-2, and SCIMACHY. In Xianghe station, CIMEL sunphotometer, gas analyzers, automatic meteorological station, and a 100-meter tower can provide aerosol optical properties, air quality status, and meteorological conditions in the planet boundary layers. The two Bruker FTIR instruments in Xianghe and Xinglong stations aim at providing the greenhouse gas such as CO₂, CH₄, N₂O, and for validation of GOSAT, OCO-2, and TanSat products in future. The FTIR in Xinglong station has been operating for more than one year, and some data has been obtained, which has been used for validation of GOSAT products.

Key words: MAX-DOAS, FTIR, NO₂, CO₂, Xianghe Station.

Global monitoring of precipitation is important because of its significant human consequences. However, the multiplicity of hydrometeor types and their small- and large-scale spatial inhomogeneities make accurate measurements difficult. For example, rain gauge measurements are significantly impaired by wind, poor global coverage, and the non-uniformity of rain. Both ground-based radars and passive microwave satellite sensors sense precipitation aloft and are generally unable to discern how much of that precipitation evaporates before impact.

The paper develops a passive sub-millimeter precipitation retrievals algorithm for Microwave Humidity and Temperature Sounder (MWHTS) onboard the Chinese Feng Yun 3C (FY-3C) satellite. The retrieval algorithm employs a number of neural network estimators trained and evaluated using the validated global reference physical model NCEP/WRF/ARTS, and works for seawater. NCEP data per 6 hours are downloaded to run the Weather Research and Forecast model WRF, and derive the typical precipitation data from the whole world. The Atmospheric Radiative Transfer Simulator ARTS is feasible for performing simulations of atmospheric radiative transfer. Rain detection algorithm has been used to generate level 2 products. Retrievals are reliable for surface precipitation rate higher than 0.1 mm/h at 15km resolution, which is in good agreement with those retrieved using the Precipitation retrieval algorithm version 1(ATMP-1) for Advanced Technology Microwave Sounder (ATMS) aboard Suomi NPP satellite.

Meanwhile, calibration and validation between similar instruments onboard different satellites are also important to ensure the validity of observations and accuracy of precipitation retrievals. In the ongoing work, we are going to carry out the calibration and validation among FY-3C MWHTS, FY-3B MWHS and ATMS.

The Environmental trace gases Monitoring Instrument (EMI) onboard Chinese high-resolution remote sensing satellite GF-5 is an imaging differential optical absorption spectrometer, expected to be launched in September of 2017. The EMI instrument will measure earthshine radiances with the wavelength range from 240 to 710 nm at moderate spectral resolution (0.3-0.5nm) at nadir. The EMI is tasked with quantitatively measuring global distribution of tropospheric and stratospheric trace gases such as NO2, O3, and SO2. The prelaunch calibration phase is essential to acquire necessary knowledge on the properties and performance of the EMI instrument as well as support data processing and retrieval. This work focus on nitrogen dioxide retrieval from on-ground measurements of gas cell and atmospheric scattering light, and an evaluation of the performance of the EMI instrument from the retrieval.