The aim of the SeRAC project is to support the absolute calibration of the altimeter onboard the Sentinel-3A and Sentinel-3B satellites using the Permanent Facility for Altimetry Calibration (PFAC) in west Crete, Greece.
Absolute calibration of satellite altimeters, during their lifetime, by external and independent facilities, such as the PFAC, is a prerequisite for a continuous, homogenous and reliable monitoring of the Earth, its oceans and its climate change. Altimetry system’s responses have to be continuously monitored and controlled for their quality, biases, errors, drifts, although relations among different missions have to be established on a common and reliable Earth-center reference system, maintained over a long period of time.
In PFAC, calibration of the multi-mission satellite altimeters takes place employing several absolute and relative calibration and validation techniques both at sea but also on land using a prototype microwave transponder (Mertikas et al., 2018). The latter operates at the CDN1 Cal/Val site that has been designed, constructed and maintained by the European Space Agency (link).
The European Space Agency’s strategy for Fiducial Reference Measurements (FRM) constitutes an effort to achieve reliable, long-term and consistent satellite Earth observations and products, via undisputable calibration and based upon metrology standards. In this context, an Action Plan towards FRM for Altimetry has been recently published (Mertikas et al., 2019).
According to this action plan, the use of a microwave profiler, to be placed at Cal/Val sites of the PFAC would be an advantage for attaining the FRM status and also an asset for wet troposphere delay (WTD) estimation that is currently carried out via dedicated GNSS (Global Navigation Satellite System) processing. This is because it constitutes an alternative and independent technique that is expected to lead us more close to the true WTD at the time of satellite overpass.
The European Space Agency provided the Radiometrics MP-3000A Radiometer to be installed at the CDN1 transponder Cal/Val site. Several preparatory works had to be performed before the instrument’s installation such as: (1) construction of a concrete base to support the instrument, (2) excavation of underground cannel to route the power and data cables from the instrument to the CDN1 equipment room, (3) upgrade the power supply and communications link systems, and (4) purchase lightning protection equipment for the instrument and the underground cables.