Background

It has long been established as "best practise" to use bright Earth surfaces, particularly deserts and playas, to validate or calibrate Earth Imagers in the solar reflective domain. Vicarious calibration of this nature was always optimum when the ground target was simultaneously calibrated by a ground team using "hand held" spectroradiometers to survey the site.  The IVOS sub-group of CEOS WGCV has recently identified a set of core sites, to serve as reference standards for this purpose called "Landnet", which have now been endorsed by CEOS plenary. 

In establishing such sites IVOS also recognised that it is essential that the measurement instrumentation and methodologies used by different ground teams across the globe was consistent and any biases understood. It therefore decided to carry out a comparison using one site as a reference.  The site chosen was a salt lake in southern Turkey called Tuz Golu, which is only dry during summer months.  This site had not been used significantly before but was very accessible.

Following an early evaluation by the site owners Tubitak Uzay and subsequently NPL in 2008, a pilot comparison involving a few selected European teams was carried out in August of this year, as a pre-cursor to a full CEOS comparison in August 2010.  The comparison in 2009 was organised by NPL, sponsored by ESA, and involved Tubitak Uzay, DLR, ONERA and CNES with observers from Brazil and South Africa.