Conference Agenda

Shadows from clouds and buildings often present in satellite images, especially in high spatial resolution satellite imagery. The Gaofen-2 (GF-2) high-resolution imaging satellite launched in 2014 has two panchromatic multispectral cameras, which is capable of collecting images with a Ground Sampling Distance of 0.8 m and 4 m in the multispectral bands on a swath of 23 km. The GF-2 provides services for high-precision land use survey. TROPOMI launched in 2017 is a satellite spectrometer with a spatial resolution of 3.5 km x 5.5 km. TROPOMI is mainly used to derive atmospheric composition products. Cloud shadows can be identified in the TROPOMI images. In atmospheric composition retrievals, clouds are usually screened and/or corrected before deriving atmospheric and surface properties. However, the cloud shadows are not flagged or corrected. On one hand, cloud shadows could lead to a bias in the atmospheric composition products if they are not corrected. On the other hand, the shadows can be used to retrieve aerosol and surface properties simultaneously.

We have developed a cloud shadow detection algorithm for TROPOMI called DARCLOS. The DARCLOS algorithm provides potential cloud shadow flags and actual cloud shadow flags. The TROPOMI actual cloud shadow flags have been verified using VIIRS images.

Because of the cloud shadow flags, we could analyse the TROPOMI NO₂ products in the shadowed pixels and in the cloud-free, shadow-free pixels to quantify the impacts of shadows on the NO₂ product. We have focused on the TROPOMI NO₂ products over Europe and China because of relatively high tropospheric NO₂ column densities in these two regions.

For the aerosol optical thickness retrievals we started with GF-2 images over Beijing. Due to the high spatial resolution of GF-2, it is possible to identify the shadows from buildings. The aerosol optical thickness is retrieved using the contrast between shadowed pixels and bright pixels and compared with AERONET data. If surface types are the same for the shadow and non-shadow pixels, surface contributions in the measured reflectances can be cancelled at these pixels. Therefore, surface albedo is not important in this algorithm, which is beneficial for the aerosol retrievals in city scale where surface albedo has large uncertainties. In principle, this algorithm can also be adapted to retrieve aerosol optical thickness using cloud shadow and non-shadow pixels.

In the presentation we will report the progresses on the cloud shadow detection, impacts of cloud shadows on the TROPOMI NO₂ products, and the aerosol retrievals using shadows.

The UK is aiming to achieve net zero emissions of GHG’s (greenhouse gas emissions) by 2050 (the Committee on Climate Change (CCC) advises in May 2019). Northern Ireland's contribution to the UK's fifth carbon budget mandates a reduction at least 35% of emissions by 2030 compared to the 1990 level. In the first phase of the project we have conducted investigations into the evolution and current status of carbon emission along with electricity generation with different type of renewable energy resources in Northern Ireland (NI). According to the national statistics, the total emissions 22 MtCO2e in 2013 across the NI was approximately 4% of the total greenhouse gas emissions in the UK, however NI accounts for 2.8% of the UK population and 2.1% of the UK GDP, hence it was concluded that the total emission of NI was more than the rest of the UK. The further results show that the NI has relatively high percentages per capita emission in the agricultural, transportation, residential, LULUCF (land use, land use change, and forestry) and power sector. In the past decades a large number of the renewable energy sites have been established across the UK and they are currently in the operation. This report will present the performance against the commitments set in the Northern Ireland Energy Strategy ‘Path to Net Zero Energy’ which includes a target to meet 70% of electricity generation from diverse renewable sources by 2030. We will present the details of the percentage of electricity generated in the NI from renewable sources as well as information about the types of these renewable sources. The report also presents a study on the relationship between the CO2 emission reduction with the power generated by renewable energy with different types of renewable energy in the NI, possible approaches of capturing CO2 emission by GHGSat.

EMPAC 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 PM2.5, 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, PM2.5 and BC is obtained from the use of an instrumented drone.
The results of the second year will be presented, including trend studies of air pollutants, newly derived NOx emissions using Sentinel 5p and the effect of COVID on the air quality in the YRD.