The EU’s Copernicus programme, with free data access to the constellation of Sentinel satellites, has pushed high resolution Earth Observation imagery data into the concept of ‘Big Data’ stimulating service providers and application developers to provide tools to harvest such free data volumes. Frequently updated, high resolution optical data is potentially available for any place on Earth every day. Data collection capabilities, on board storage and a global network of downlink stations, have radically reduced the barriers and restrictions of the past on the application of satellite imagery. What a great opportunity to utilise Earth Observation on a scale not seen before.
Since its inception over 15 years ago, the EO industry has also seen an increased provision of very high resolution satellite data (1m GSD or better) from a number of providers in the commercial satellite sector, but such data comes at a cost. Whilst the availability of high resolution satellite data (10m up to 1m GSD) is now better than ever, the question still needs to be asked: do we really need all that new very high resolution capability? Since users have to pay commercial rates, does very high resolution data represent value for money or is high resolution data like that available from the new 10m Sentinel-2 set the norm with enough information for most applications? The answer is, like for many things in life, not ‘yes’ or ‘no’, but a bit of both, application and requirement depending. In most cases a very high resolution dataset should be part of any baseline mapping exercise to fully understand an area in question. Also, when looking at a regional or country-wide scale, very high resolution will be expensive to acquire – especially when used at high temporal frequency. But for a monitoring program a lower spatial resolution data set may be sufficient. If a change or something unusual has been detected, another very high spatial resolution dataset may resolve the question and enable fully effective analysis and action.
Sentinel2, launched by the European Space Agency to meet the need for high spatial resolution optical data, is well suited to mapping large areas, detecting changes on land, and providing a dependable baseline map of wide areas of interest. However, illustrating the difference that can be made by acquiring supplementary very high spatial resolution data, is recent satellite imagery acquired over a farm area in central southern France. Showing the location, where Sentinel2 data was acquired only 2 days apart in August 2016, when looking with very high resolution (1m GSD) DMC3 satellite data, it is possible to identify the spatial detail in the local agricultural pattern and even differentiate a vineyard from neighbouring planting. Such a level of insight is simply not possible at 10m resolution, but it also may not be necessary for each data acquisition occasion in a monitoring program. Broad questions and outcomes are addressed on a regional scale. But once distinct change is detected in the regular pattern of a monitoring program with Sentinel2, an investigation of that change using very high resolution satellites will make a particular image far more detailed and insightful.
Sentinel2 provides a wide area baseline for monitoring and change detection, DMC3 delivers a powerful capability to ‘zoom in’ adding additional value to services and applications.
Figure 1: DMC3/TripleSat satellite image subset from August 2016, over an area in south-west of France near LaBastide d’Armagnac, an agricultural region producing a variety of produce incl. some vineyards. Copyright: 21AT/Earth-i