| Summary: | Remote sensing has become an important tool for monitoring the Earths environment. Considerable climate changes will probably take place in the nearest future, especially around the polar areas. To be able to use satellite images of the polar regions, the atmospheres composition and the spectral properties of the ground will have to be examined. This has already been performed for large parts of the Earth, but not in the same extent in polar and sub-polar areas as in the equatorial regions. The work described in this report is a part of the Nordkalotten Satellite Evaluation co-operation Network (NorSEN). The main goal for project NorSEN is the establishing of a network for satellite data validation in the Arctic and sub-Arctic regions. For reaching this goal NorSEN includes stations for performing spectral measurements on different sites within the sub-Arctic region. One of these stations is described and evaluated here. The main purpose of this report is to process, analyse and evaluate data from ground based measurements. This, to be able to use the data in later comparison with satellite data. To perform ground based measurements a raft was placed on lake Torneträsk, which lies in the sub-Arctic region in Sweden’s northern parts, during three months in the late summer 2005. The raft was equipped with three spectrometers for measuring downwelling irradiance from the sky, downwelling radiance from a small part of the sky and upwelling radiance from a column of water in the lake. Torneträsk is a large and very clear lake with not much pollution and was therefore selected to be a possible reference surface for satellite image validation. Issues like sun glint, weather, waves, shadows and particle flows into the lake were investigated. The reflectance, i.e. the amount of incoming radiation reflected from somewhere inside the water column, was studied since it can be compared to spectral satellite data. Particle flows into the lake clearly effected the reflectance and it also differed between clear and cloudy days. ...
|
|---|