Tuz Golu: new CEOS reference standard test site for infrared visible optical sensors

Tuz Golu, a dry salt lake located in the central plateau of Anatolia (38.50 degrees N, 33.20 degrees E, center latitude longitude) in Turkey, was established as a standard reference test site for the vicarious calibration of land surface imagers. The site was first selected on the basis of the spatial uniformity results from the analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) images from July-August 2004 and July-August 2006. This proved its suitability for the calibration of high-and medium-resolution optical sensors. During the 2008 and 2009 measurement campaigns, the site was characterized in terms of its solar spectral surface reflectance factor (RF) and surface bidirectional reflectance factor (BRF) characteristics and atmospheric conditions. The average surface reflectance factor is between 0.4 and 0.6 in the visible and near infrared (VNIR) and about 0.2 in the short-wave infrared (SWIR), which makes this site suitable mainly for the VNIR spectral region. The site is spatially uniform to within 2%-4% normalized standard deviation in the VNIR with large homogeneous areas, which are suitable for the calibration of medium-resolution optical sensors. The aerosol optical thickness at 550 nm has values higher than 0.1, and the related Angstrom wavelength exponent has values over 1.3 for most of the days during the 2008 and 2009 measurement campaigns, indicating the presence of anthropogenic aerosols. According to the meteorological data (rain, solar irradiance) and the availability of large, dry homogeneous surfaces in August, the site can be used for postlaunch calibration of land surface imagers at this time of the year. It is one of the eight instrumented reference standard test sites (LandNet) that is characterized on a yearly basis by TUBITAK UZAY (TU), Turkey, with traceability to the International System of Units (SI) standards through the National Physical Laboratory (NPL), United Kingdom, according to the satellite overpasses. The data can be provided to interested space agencies on request.