The amount of Earth Observation (EO) data and derived products is increasing rapidly in terms of volume and variety. Today satellite remote sensing EO data have already exceeded the petabyte scale and are increasingly freely and openly available from different data repositories, hubs and catalogues. The data in these sources are processed at various levels ranging from level 0 (raw data) to level 4 (combination of multiple lower level data) and produced in different data formats. Visualization and processing of these data is an issue for many users. Several software and tools are available, some are commercial, while others are low cost or free. The choice of tool also depends on how advanced functionality the users needs. Here we present QGIS as an open source software tool which can be installed on all major operating systems and doesn’t require strong previous knowledge in processing and visualization from the users. The data used is from NEXTGEOSS Cold Regions pilot.
QGIS is an open source geographical information system (GIS). The program can visualize, manage, edit, analyse data and produce a printable map in most common formats, there are also numerous plug-ins that extend the functionality of QGIS. The program has tools to read both vector and raster data. Standard installer packages are available for MS Windows and Mac OS X. For many flavours of GNU/Linux, binary packages (Red Hat and Debian) or software repositories are provided to add to your installation manager. Get the latest information on binary packages at the QGIS website
Sea ice data
Sea ice data from satellites represent one of the longest Earth Observation records from space. The variations of sea ice compared with the surrounding open water with respect to temperature, emissivity and reflectivity make it an ideal case for remote sensing. Today several sensors and techniques have been developed producing sea ice data at different spatial and temporal resolutions. Sea ice concentration has been produced from microwave radiometers since the 1970s. Radar Altimeter from ERS, Envisat, ICESat and Cryosat-2 has been analysed to retrieve large scale ice thickness. Several sensors are used to retrieve ice drift at different resolution Scatterometer, Radiometer and Synthetic Aperture Radar (SAR). Operational ice services use SAR in combination with optical sensors for producing ice chart manually. The ice charts are mainly used for planning within offshore operation and shipping community. Most of these data are available through different portals and catalogues.
In this demonstration we used ice/water classified Sentinel-1 images NextGEOSS Cold Region pilot and the ice chart from the Copernicus Marine Environment Monitoring Service (CMEMS). CMEMS provides regular and systematic reference information on the physical state, variability and dynamics of the ocean and marine ecosystems for the global ocean and the European regional seas. The data can be accessed and downloaded from the CMEMS catalogue at http://marine.copernicus.eu/– The data policy of CMEMS is to provide full, free and open access to its products. The CMEMS catalogue is covering all the Copernicus marine data: Sea Surface temperature, Salinity, Current, Wind, Sea ice, Sea level, Biology, Chemistry, Chlorophyll etc.
The demonstration originally consists of three parts;
- Visualizing Ice concentration data from CMEMS using QGIS, here we introduce QGIS by visualize and create a map from CMEMS data (sea ice concentration) with standard map elements like map inset, grids north arrow, scale bar and labels.
- Accessing and Downloading CMEMS data; here we show how to get access and download CMEMS as one of the main catalogues providing EO data, then visualizes the data in QGIS and produce a map.
- Comparing Data from NextGEOSS and CMEMS using QGIS; here we used sea ice edge in Fram Strait from two different data sets: (1) Ice-water classified from Sentinel-1 images (2) the ice chart from CMEMS produced. The images and the chart are from the same day using image contrast and layers overlay on QGIS 3.8.
In the webinar the three parts are condensed and presented in two parts (slides). First QGIS was introduced with consideration that the software is already installed. There are two ways for the users to start working with QGIS, get the project with all needed data ready and directly open it in QGIS or let the user start their own project by loading the data and save the project. An already prepared project is used to demonstrate that, where a sea concentration data is presented. Then two important features from QGIS are presented, project properties where information of the project is found these are metadata, coordinate system, data sources and many others. The other feature is the layer properties which can be accessed by right clicking on the layer under layers sub-window. There are several layer properties; information from provider, extent, units, width, height, location composition (number of bands). Also Render type, Band and colour ramp (where the colour used in the layer can be defined).
The second part in the webinar is used for comparing sea ice data from NextGEOSS and CMEMS using QGIS. The main steps are:
- Search and Download data
Step by step procedure is presented for downloading data from CMEMS http://marine.copernicus.eu and that is by define regional domain (arctic ocean), parameters (sea ice) and date (from 20 July to 23 July 2018) then the sea ice concentration charts is downloaded in NetCDF format. For the sea ice edge images is downloaded from NERCS, http://thredds.nersc.no/thredds/catalog.html
- Visualization using QGIS
Start QGIS, since data from the Arctic is used, make sure that the data are projected correctly when loaded to the QGIS, do that in the project properties. In the Coordinate Reference System (CRS) in the filter search for EPSG:102018 then select North_Pole_Stereographic, then apply. First data from CMEMS is uploaded then layer properties is used to select the data from the 23 July, 4 layers from the 20 July to 25 July 2018 are available (expected to be 6 layers and since the chart is not produced on the weekend 21 and 22 July are weekend days) so the dates of the layers are 20, 23, 24 and 25 July. Then symbology is used to pick the colors and the background for the layer. The three images are then uploaded.
- Simple Processing in QGIS
To work with images properties, each image will be treated separately, and that will take longer time and all the process should be done the same. The other alternative and more productive is to mosaic the three images in one image by merging the images. Before doing that, the images have to be saved as GeoTIFF files. Then the merge tool in processing ‣ TOOLbox ‣ GDAL ‣ Raster miscellaneous is used.
- Comparing the data sets
To compare the ice edge from the CMEMS ice chart and the ice edge image two approaches are used
- Image symbology and contrast
- Create a shape file by tracing the ice edge from the image and overlay it on the ice chart map
- Making Maps
Create print layout is used to create a map from the ice concentration chart and the ice edge images. The maps can be exported to several formats image, SVG and PDF formats. The exported maps can be used directly in reports publication etc.
1- Visualizing Ice concentration data from CMEMS and making Maps using QGIS <link>
2- Accessing and Downloading CMEMS data and visualize in QGIS <link>
3- Comparing Data from NextGEOSS and CMEMS using QGIS <link>