Conference Agenda

About 70% of the Earth is covered by clouds, therefore clouds are often present in satellite observations. Cloud properties can be retrieved from satellite observation. Cloudy pixels are often screened before deriving atmospheric and surface properties. In the satellite products, cloud is typically assumed as a horizontal homogeneous layer. However, in reality cloud is a three dimensional (3D) object: clouds cast shadows on the ground surface or on lower clouds; clouds look brighter on the sun illuminated side and darker on the shadow side. The impacts of 3D cloud features on aerosol retrievals have been studied using high resolution satellite imagery data and lidar measurements. Clouds are also important in the trace gas retrievals. The research on the 3D cloud effects on trace gas retrievals is a new topic because the pixel size of the satellite spectrometers like GOME-2 is too big (40 km x 80 km) to see the 3D cloud effects. Since the launch of Sentinel-5p (S5p) in 2017, the trace gases are retrieved at a pixel size of 3.6 km x 5.6 km. We have seen the cloud shadows on the S5P images, which indicates the present of 3D cloud features in the S5p products. The objectives of the project are to analyze the impacts of the 3D clouds on trace gas retrievals, detect the cloud shadows, and derive aerosol and surface albedo products. Aerosol properties and surface albedo are important input parameters in the trace gas retrievals. Aerosol optical thickness (AOT) and surface albedo will be retrieved for selected scenes using the cloud shadow pixels. This is a complimentary method for the general used method nowadays. The algorithm will be demonstrated using Sentinel-2, Sentinel-5P, GF-1/6. The retrieved AOT will be validated from ground-based measurements and compared with Sentinel-3 aerosol products.We will detect cloud shadows from S5p and compared with collocated VIIRS data. The high resolution imagery of VIIRS will provide more accurate detection of cloud shadows and cloud edges on the S5p data. From selected scenes we will study the variation of trace gas column densities with the distance to the clouds. We will use the 3D radiative transfer components of the Earth Clouds and Aerosol Radiation Explorer (EarthCARE) simulator (ECSIM) together with 3D high resolution cloud fields generated using Large-Eddy Simulation (LES) model to simulate S5p/TROPOMI measurements. The simulations will help us to understand the shadow and the 3D cloud effects on the TROPOMI cloud, Absorbing Aerosol Index (AAI), AOT, and nitrogen dioxide (NO2) products. Ultimately, we plan to correct the impact of 3D clouds (shadows) on the Sentinel-5p/4/5 products. The project will use Sentinel-2/3/5p, GF-1/6 products and can be applied to S4/S5 after they are in orbit.The deliverable are reports, publications, and demonstration products and data analysis results. The KNMI team is partly supported by the User Support Programme Space Research of Dutch Research Council and KNMI internal funding. The IAP/CAS team is supported by IAP internal funding.The topic is Atmosphere. Subtopic is related to air quality but also related to greenhouse gases because the greenhouse gas products from satellite observations will also be impacted by 3D clouds and shadows.

The growth rate of atmospheric carbon dioxide (CO2) reflects the net effect of emissions and uptake resulting from anthropogenic and natural carbon sources and sinks. The anthropogenic emissions of CO2 are primarily generated by human activities, including fossil fuel combustion, energy used in transport sectors, etc. In the urban, energy used in domestic and transport sectors takes more than 80% of the total energy consumption in the UK. In the past decade, renewable energy (RE) technologies, such as solar and wind power, geothermal and hydro power, have gradually been deployed in domestic buildings for heating and electricity. However global fossil CO2 emissions are still more than 4% higher in 2019 compared with those in 2015. In the UK, the recent campaign of CO2 reductions has proposed a policy of the phase-out of coal, and by 2050, the gas boiler could be as obsolete as the coal fire in UK homes. Although many policies for decarbonisation, like the Paris Agreement and integrating REs into urban buildings have been introduced, it is not clear what is the contribution of REs to CO2 reduction. Therefore it is imperative to study the impact of new RE integration with existing power generations on the CO2 reduction by using satellite monitoring, RE demand site response and artificial intelligent technology.

Since 1983, the World Meteorological Organization (WMO) has established various Global Atmosphere Watch stations worldwide in different latitudes and longitudes to continuously monitor changes of atmospheric CO₂and CH₄ concentrations at near-surface level. Several satellites have been launched, including Japan Greenhouse gases Observing Satellite (GOSAT), NASA OCO-2 and OCO-3 satellites, and Chinese carbon dioxide observation satellite (TanSat). These satellites provide the ability to retrieve XCO2, and their XCO2 data products have been used to improve our knowledge of natural and anthropogenic CO2 sources and sinks. The synergistic use of complementary measurements is not only addressing the carbon cycles, but also opens a unique opportunity to address some of the main knowledge gaps in atmospheric CO2 for the urban with the prevision of integration of REs into buildings for electricity and heating.

The report will present the project objectives and initial progress of the project, including the preparation of satellite data, the distribution of renewable resources and energy demanding over the urban areas,and the latest provisional estimates of regional greenhouse gas emissions based on provisional inland energy consumption statistics.

The EMPAC project addresses different aspects related to the air quality (AQ) over China: aerosols, trace gases and their interaction through different processes, including effects of radiation and meteorological, geographical and topographical influences. Satellite and ground-based remote sensing together with detailed in situ measurements provide complimentary information on the contributions from different sources and processes affecting AQ, with scales varying from the whole of China to local studies and from the surface to the top of the boundary layer and above. Different species contributing to air quality are studied, i.e. aerosols, in AQ studies often represented as PM_2.5, trace gases such as NO₂, NH₃, Volatile Organic Compounds (VOCs) and O₃. The primary source of information in these studies is the use of a variety of satellite-based instruments providing data on atmospheric composition using different techniques. However, satellite observations provide column-integrated quantities, rather than near-surface concentrations. The relation between column-integrated and near-surface quantities depends on various processes. This relationship and the implications for the application of satellite observations in AQ studies are the focus of the EMPAC project. Detailed process studies are planned to be undertaken, using ground/based in situ measurements, instrumented towers, as well as remote sensing using lidar and Max-DOAS. A unique source of information on the vertical variation of NO₂, O₃, PM_2.5 and BC is obtained from the use of an instrumented drone.
The results of the first year will be presented, including newly derived NO_x emissions over the Yangtze River Delta from the Sentinel 5P satellite.

The aim of this project consists in the development and application of processing methodologies to address two specific Sub-topics relevant for stack-based spaceborne applications. Sub-topic 1 concerns the internal structure of natural media, and it is mapped to Dragon topic Solid Earth - Subsurface target detection. Sub-topic 2 concerns joint estimation of deformation and water vapour maps, and it is mapped to Dragon topic Solid Earth - Monitoring of surface deformation of large landslides. The topics above are of fundamental importance in the context of present and future spaceborne missions, which will allow increasingly more systematic use of multiple acquisitions thanks to improved hardware stability and orbital control. Indeed, the proposed activities are intended to support use of multi-pass data stacks from:

• the upcoming P-Band mission BIOMASS.
• future L-Band missions, such as the SAOCOM constellation, the upcoming Chinese L-Band bistatic Mission Lu-Tan1, and potentially Tandem-L and Rose-L.
• the C-Band Sentinel Missions.

Sub-topic 1 will consider as test sites a forested area in North-West Germany and a desert area in Namibia, which are under study in the context of the ESA campaigns TomoSense and DesertSAR. The activities will focus on processing SAR image stacks to extract information about forest structure and sub-surface terrain topography on forested areas, and about the internal structure of sand dunes and surface topography on desert areas. Estimation and compensation of ionospheric and tropospheric propagation effects will be considered as well. Given the availability of a large amount of reference data at both sites, the success of this study will be assessed by direct validation against reference data from in-situ measurements and products from airborne Tomography.

Sub-topic 2 will consider: Kenya or South-Africa, of interest for retrieval of water-vapor and deformation over large scale, and other suitable test sites,. The objective is two-fold. For the generation of tropospheric products, for meteorological application, the synergic exploitation of distributed and permanent scatterers, is still an open issue, where the retrieval of absolute phase screen needs merging with GNSS and meteorological maps (ERA5, GACOS), where timeliness and efficiency is a must. The integration of DS and PS will in parallel by tested on difficult sites.

Earth’s climate is influenced profoundly by anthropogenic greenhouse gas (GHG) emissions. The lack of available global CO₂measurements makes it difficult to estimate CO₂ emissions accurately. Satellite measurements would be very helpful for understanding the global CO₂ flux distribution if CO₂ column-averaged dry air mole fractions (XCO₂) could be measured with a precision of better than 2 ppm. To this point, the main objectives of this research project in Dragon 5 is to use a combination of ground-based measurements of CO₂ and CH₄ and data from current satellite observations (TanSat, GOSAT/-2, OCO-2/-3 and TROPOMI) to validate and evaluate satellite retrievals with retrieval inter-comparisons, to assess them against model calculations and to ingest them into inverse methods to assess surface flux estimates of CO₂ and CH₄. In this presentation, we will introduce the 1^st global map of carbon flux from the new TanSat XCO2 product by an ETKF data assimilation system coupled with GEOS-Chem CTM. The error reduction compared to a priori indicates the benefit on carbon flux estimation after assimilating global satellite XCO2 measurement, and the carbon flux distribution over global changed through the whole year from May 2017 to April 2018. A new SIF product also produced by IAPCAS and a comparison with OCO-2 measurement shows a comparative result. Ground based long-term measurement by automatic running of EM27 is performed at IAP building in Beijing from 2019 which has been used in satellite measurement validation and city carbon monitoring. We will also show the new results and progress on next generation TanSat mission.

The purpose of project ‘Monitoring of Greenhouse Gases with Advanced Hyper-Spectral and Polarimetric Techniques’ is to improve the accuracy of the greenhouse gas products XCO2 and XCH4, inferred from the combination of hyper-spectral satellite measurement and polarization satellite measurement in close collaboration between the Chinese and European partners. In the first year, we have done the works as following:
1 We have collected three types of data we need, satellite global measurement data such as GOSAT, OCO-2, POLDER, GMI and DPC and so on, auxiliary data such as MODIS products and ECMWF reanalysis data, and validation data such as TCCON data and products of GOSAT and OCO-2.
2 Chinese scientists have developed the atmospheric CO2 retrieval method for clear sky measurements, which contains atmospheric radiative transfer calculate module, environmental data preprocessing module and retrieval module. We tested the method using GOSAT data and the result shows that the method is able to retrieve the hyper-spectral measurements.
3 European scientists have developed the retrieval method for a synergistic retrieval of aerosol properties and XCO2 column mixing ratios. The software is tested extensively on GOSAT data with global coverage and retrieval shows encouraging results.
In the next year, our main works include improving the retrieval method developed by Chinese scientists and studying the joint utilization of polarimeter and spectrometer observations. With the support of European scientists, we will improve the radiative transfer calculation, key parameters setting, iteration updating strategy and results correction, to make the retrieval method fit for GMI instrument characteristics better. In parallel, European scientists will research on the joint utilization of polarimeter and spectrometer observations, develop the retrieval method and analyze the improvement in greenhouse gases retrieval. Through on-line academic exchanges, visiting terms if permitted and annual reporting of Dragon 5 program, young scientists will improve their academic level through the project.