Conference Agenda

A ground-based 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 operated in Xinglong Station. Two PICARRO G2301 instruments carry out simultaneous measurement for surface CO₂ concentration. Also, there is a MAXDOAS instrument in Xianghe, which 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. The two Bruker FTIR instruments in Xianghe and Xinglong stations aim at providing the greenhouse gas such as CO₂, CH₄, N₂O, and for validating GOSAT, OCO-2, and TanSat products in future. The FTIR in Xianghe Station is now doing conventional observation of CO2 and CH4 concentration, providing a high quality dataset for validating the CO₂-measuring satellites over the world.

Key words: FTIR, PICARRO, CO₂, CH₄, Xianghe Station

As the improvement of high temporal, spatial, spectral resolution optical sensor technology, remote sensing becomes a more and more important way to understand the status and changing in both local and global scale. How to accurately calibrate the remotely sensed data becomes one of the primary problems before remotely sensed data used in different quantitative researches and applications. Consistency transfer calibration, which the measurement benchmark is obtained with ground-based and airborne standard instrument and then transferred to satellite sensors, is an efficient approach to improve the quality of satellite remotely sensed data, and it is also a key technology for operational application of the space-borne radiometric measurement benchmark. The composition of the calibration system includes: 1) the ground-based and airborne hyperspectral imager, 2) the matchup of different observation elements between different observations and 3) the standard transfer technology. Supported by the National High Technology Research and Development Program of China, the whole system has been established. And consistency transfer calibration field campaigns have also been carried out to comprehensively validate related sensors, targets and methods.

1) Totally three ground-based hyperspectral imagers and three airborne hyperspectral imagers have been developed, covering VNIR (400-1000nm), SWIR (1000-2500nm) and TIR (8-12.5μm). The spectral resolutions are 2nm, 5nm and 40nm for VNIR, SWIR and TIR ground-based imagers, respectively, and 3.5nm, 10nm and 80nm for VNIR, SWIR and TIR airborne imagers, respectively. The total field of view (FOV) of ground-based imagers is 22°, and that of the airborne imagers is up to 60°. All of the imagers have self-calibration units to guarantee the performance under actual working conditions.

2) Multi-scale data multi-element matchup methods have been developed. A spatial registration method for large resolution difference images has been proposed. The spectral matchup methods for two hyperspectral imagers and for hyperspectral imager to multispectral imager have been developed. Angular normalization models were built up for reflective solar band (RSB) and thermal emissive band (TEB), respectively. Sensitivity analysis and uncertainty analysis were performed for these methods and models.

3) Considering difference in atmospheric radiative transfer processes for different bands, consistency transfer calibration schemes were designed for RSB and TEB, respectively. Through uncertainty analysis on field non-uniformity, surface BRDF and radiative transfer calculation, the total accuracy in transfer calibration is shown to be better than 5% for RSB, and better than 1K for TEB. As to spectral calibration, the method based on atmospheric absorption lines was adopted, and brings out calibration accuracy better than 0.5nm for RSB, and better than 8nm for TEB. These indices can satisfy the specification of this sub-project.

In the last September, consistency transfer calibration experiments were carried out in the National Calibration and Validation Site for High Resolution Remote Sensors (the Baotou site). The artificial targets and natural scenes were employed as reference. More than 60 air lines were flied acquiring airborne data. Ground measured hyperspectral imager data, surface feature measurement data and atmospheric measurement data were simultaneously obtained during the flight. Overpassed high-resolution satellite data (Sentinel-2B, SV1) were used to validate the whole system. Results indicate that the total transfer calibration chain is basically feasible and reasonable. The advantages of consistent transfer radiometric calibration technology include: Firstly, in benchmark obtainment, the “ground truth” covering large area can be obtained rapidly. Therefore, the errors due to the heterogeneity of surface and temporal variance of environment can be efficiently decreased. Secondly, the airborne imager can be comprehensively calibrated by the self-calibrator and “ground truth” measured by ground-based imager so as to decrease the uncertainty. However, lots of work is still needed to improve the system, and the uncertainty traced to SI should be analyzed much more elaborately with more experimental data.

The nadiral satellite-based brightness observations were made using the Microwave Humidity and Temperature Sounder (MWHTS) instrument aboard the FY-3C polar-orbiting platform since Sept 30, 2013. Separate retrievals are demonstrated for mid-latitude conditions in extreme weather. The retrieved profile root-mean-square errors are about 0.9 K with bias error less than 1.5K. These are substantially smaller than the a priori temperature profile variations, demonstrating that 118-GHz aircraft or satellite observations can provide useful information on atmospheric vertical thermal structure. Combined with 183GHz and window channels, water vapor profiles are also retrieved accurately to be used in Sandy typhoon data assimilation model.

This paper is organized as follows. The microwave instrument is first introduced, and it is demonstrated that multiple receiver arrays can be used to multiplex a large set of channels onto a single spot on the ground. We next point out that opacity due to water vapor continuum absorption is a fundamental limitation of conventional millimeter-wave sounding and show how a multi-channel millimeter-wave approach can be used to complement the temperature-sensitive observation and overcome this limitation. We then adapt two methods to realize data assimilation based on profiles and radiance separately and in combination, and then compare with current impact in WRFDA model. Temperature, water vapor, and precipitation retrieval performance comparisons are then presented, and the impact of correlated error sources on performance is examined. Finally, we summarize and provide suggestions for further research and development of data application about polar-orbital satellite.

We present work on use a compact solar-tracking Fourier Transform Spectrometer (Bruker EM27/SUN) to precisely derive total column averaged amount of Greenhouse gases.

In order to ensure the high quality of the retrieved data, XCO₂ measured from Bruker EM27/SUN are compared to well calibrated IFS125HR in Xianghe (39.798˚N, 116.958˚E, 50m a.s.l.) as reference. We also processed the EM27/SUN data using PROFFAST and GGG2014 for further investigation the performance of the EM27/SUN. The comparison between EM27/SUN and IFS125HR shows a 0.24% bias with GGG2014+EGI, while a bias of 0.53% approached by PROFFAST. To further characteristics the differences between the two algorithms, Xgas has been measured by EM27/SUN in Beijing (IAPCAS) with coordinate weather record by WS500 weather station. The GGG2014 and PROFAST are involved in data processing, but found a bias of 0.20%, 1.23%, -1.0% for XCO₂, XCH₄ and XCO respectively. X_air calculated by the above two algorithms are approximately 1.0012、0.9831. The correlation coefficient is 0.9979 for daily median XCO₂ between the result of these two retrieval algorithms. Reasons for these differences could be attributed to the difference in pre-processing method, solar model, instrument lines shape model, gas spectroscopy.

Furthermore, field campaign collaborating EM27/SUN and aircore soundings will contribute to the greenhouse gases validation for TanSat, Sentinel-5P as well as other greenhouse gas satellites, GOSAT and OCO-2.

The surface albedo characterizes the ability of the Earth's surface to reflect solar radiation. It is an important land surface characteristic parameter that affects the radiation and energy balance of the Earth system, and determines the distribution process of radiant energy between the Earth's surface and the atmosphere. This study aims to use the Chinese FY-3C polar-orbiting meteorological satellite data to invert and verify the surface Albedo.

The inversion algorithm uses the RossThick-LiTransit semi-empirical kernel-driven BRDF (Bidirectional Reflectance Distribution Function)model, and uses the constrained least squares method to fit the model coefficients , and . The BRDF of any zenith angle and observation angle can be obtained by nuclear extrapolation . The BRDF is hemispherically integrated in the observation direction to obtain the narrow band BSA(Black-Sky Albedo) of the FY-3C band 1-4,and the double hemisphere integral is obtained in the incident and observation directions to obtain the narrow band WSA(White-Sky Albedo) of the FY-3C band 1-4.The 6S atmospheric radiation transmission model is used to simulate the surface downward radiant flux and the surface upward radiation flux covering a variety of atmospheric conditions, multiple observation angles, and various BRDF characteristics, so as to obtain the broadband albedo albedo of visible band.Using the method of multiple linear regression analysis, a linear conversion equation between narrow band albedo and broadband albedo is constructed. Using this equation, the broadband albedo of the FY-3C MERSI visible band (0.4-0.7 μm) can be obtained.

The clear sky Data of FY-3C surface albedo data, MODIS-MCD43A3, CGLS-SA and GLASS-ABD in the study area were randomly selected as the verification data, and the correlation analysis, absolute deviation analysis and root mean square error analysis were performed with these surface albedo product data. It can be seen intuitively from the scatter plot that the scatter distribution of the FY-3C surface albedo product and MODIS-MCD43A3, CGLS-SA and GLASS-ABD surface albedo product are relatively regular. The four surface albedo products have good consistency in narrowband and visible band, the correlation coefficient is about 0.88, the overall absolute deviation is 0.068, and the minimum root mean square error is 0.02, indicating FY and MODIS-MCD43A3, CGLS-SA and GLASS-ABD Have a high degree of fit.The causes of the differences in the surface albedo data verification were analyzed: (1) After geometric revision, there is a geometric error of 2~10 pixels in the MERSI reflectivity data, and the surface reflectance inversion using 16 days of clear sky data will produce a large error where the underlay surface is not uniform. (2) There is a difference between the surface reflectivity data of FY-3C after atmospheric correction and the surface reflectivity products such as MODIS-MCD43A3, CGLS-SA and GLASS-ABD, which leads to the difference of inversion.

The results showed that the surface albedo products of FY-3C and MODIS-MCD43A3, CGLS-SA and GLASS-ABD showed good correlation. The inversion algorithm of FY-3C surface albedo still needs to be studied deeply, and the improvement of inversion accuracy also depends on the key links such as data location, atmospheric revision and so on. In addition, the FY-3C surface albedo verification also needs to use the ground station point measured data for further comparative analysis.