The main purpose of Earth observation campaigns is to support the preparation of future satellite missions and to validate the data from those in orbit.
Before embarking on building a large satellite mission, it is important to make sure that the instrument under consideration is not only capable of providing remotely sensed information, but also that it will achieve the accuracy required. This cannot always be done by scientific studies alone.
Therefore, real measurements and images are acquired by sensors on aircraft, on ships and from ground-based equipment as well as from laboratory instruments.
During the development phase of a typical mission, campaign data are also needed for the development of interpretation methods, calibration concepts and the refinement of processing algorithms.
One a satellite is in orbit and operational, field campaigns are organised to collect independent measurements to compare with the satellite data productions for validation purposes.
In essence, campaigns are carried out to:
- Explore Earth observation possibilities
- Prove concepts
- Develop interpretation
- Develop calibration
- Simulate data products
- Validate results
Campaign requirements are associated with different objectives for technology, geophysical modelling, simulation and validation. However, this invariably means venturing out into the field to carry out intensive measurement campaigns.
Recent campaigns include large international efforts in the Arctic to validate the CryoSat and SMOS missions, and an airborne campaign over Germany that used the same technique proposed for the candidate CarbonSat Earth Explorer to measure atmospheric carbon.
The main technological requirements for campaigns involve testing new technologies from aircraft and the improving the performance specifications for future space-borne missions. New technologies tested on airborne platforms and from ground sites include multiband, polarimetric synthetic aperture radars and interferometers, imaging spectrometers, microwave radiometers, radar altimeters, microwave limb sounders, lidars, and rain/cloud radars. Data from campaigns are used to help the specification of future spaceborne instruments, algorithm development and planning validation.
The main objective of geophysical modelling is to develop operational algorithms for Level-2 products from spaceborne sensors. Level-2 products are obtained through a conversion from calibrated sensor outputs in terms of physical variables (backscatter coefficient, reflectance, brightness temperature) to target characteristics (ocean wind and waves, suspended matter, biomass and soil moisture on land, trace gas concentration in the atmosphere). This is complex and takes time. It involves a learning process both inside ESA and within the potential user community. Its importance however, cannot be overestimated.
Simulation provides datasets to ESA engineers and the scientific and applications user community for training and testing purposes. In many applications, the end user can only be satisfied with higher than Level-2 products, whereby the Level-2 products are assimilated with other, non-satellite data. Campaigns have proven to be the ideal vehicle for involving the end-user community in the early development of these assimilation schemes. After initial analysis of these datasets as reported during the final campaign workshops, they are available as inputs for definition studies and algorithm development work.
Calibration and validation
Following internationally agreed definitions, instrument and data calibration involves pre-launch and post-launch measurements to fully characterise the payload instruments and subsequent activities to configure the ground processors to provide calibrated (Level-1b) data products such as radiance, reflectance, transmittance, polarisation and radar backscattering coefficient. Through geophysical calibration and validation Level-2 products are derived and checked against independent in-situ measurements of the relevant geophysical variables. These include atmospheric variables (temperature, pressure, atmospheric constituents, and aerosol and cloud parameters), marine variables (ocean surface wind and waves, ocean colour, sea-surface temperature, sea-ice thickness, ocean salinity) and land variables (vegetation index, temperature, pressure and reflectance). For each geophysical data product, a number of different in-situ measurements are made using ground-based and airborne. After the commissioning phase of a typical mission, the validation programme will make a quality assessment of the geophysical data products and will recommend re-calibration and algorithm development as appropriate.