CALIBRATION service - on-request service
|Last update: March 2017|
We provide on-demand long-term time series calibrated using short-term in-situ measurements.
The long-term time series are usually extracted from our satellite-derived solar radiation database HelioClim-3. However, we are also able to apply our calibration procedure on data from another provider.
The short-term in-situ measurements are either provided by the Customer, or retrieved or bought from a nearest ground station. If the data are provided by the Customer, we agree to sign a Non Disclosure Agreement document to protect the confidentiality of your data.
Whatever the data used as inputs to our calibration procedure, the steps are the following:
1_ Quality check of the ground measurements
We apply a careful quality check procedure onto the data, following the outcomes and recommendations of the European project ENDORSE. For more details on the quality check procedure, please refer to the ENDORSE report on the harmonization and control of meteorological data (D 3.2), and get a good summary in the poster Espinar et al. 2012.
The quality check procedure aims at identifying non plausible data and outlyers. A flag is provided with the returned data to inform with different degrees of plausibility. If the number of plausible data is insufficient, the calibration is not applied, and the Customer is informed by Transvalor that the calibration procedure is not possible with these data.
2_ Assessment of the discrepancy prior calibration procedure
Once the quality of in-situ measurements has resulting in a sufficient number of plausible data, the discrepancy between satellite and in-situ measurements is assessed on the temporal period of the in-situ measurements. Several indices are computed to get a reference of the performance for the coming-next calibration.
3_ Calibration procedure
The calibration procedure has been originally designed and validated during the Atlas PACA project. Afterwards, the procedure has been empirically fine-tuned to fulfill the requirements of the users. The method uses a non-linear expression, which takes into account the day in the year. The results is a set of parameters estimated on the temporal period when the in-situ measurements are available, and then applied on the long-term satellite radiation values.
4_ Assessment of the discrepancy after calibration procedure
The discrepancy is computed between the in-situ measurements and the calibrated satellite data on the temporal period of the in-situ measurements. The performance of the calibration procedure is given by comparing the discrepancy before and after the calibration procedure.