Frequently Asked Questions

CalVal Portal

Q: What is the purpose of this web page?

A: please read here

MERIS L1b Data

Q: Are MERIS L1b data smile corrected?

A: No. MERIS has 5 cameras, each with a CCD camera which measures in one dimension one line across the flight direction and samples the spectrum in the other dimension. This means that along a line in the image, each pixel corresponds to one detector in one of the 5 cameras, and each detector is measuring at its own wavelength, which is close to the nominal one of the spectral band. However, there is a small difference in wavelength among each camera (<0.1nm) and across the cameras (~ 1nm). This difference is called the smile effect and is seen as striping in the images. Data tables are available which specify the wavelength of each detector.

Q: Can the saturation occur?

A: Yes, over clouds some bands may be saturated.

Q: What is the accuracy of the geolocation?

A: The accuracy is ~ 250m, which is 1/4 of a pixel for RR data and ~ 1 pixel for FR data. A tool has been developed (AMORGOS), which improves the accuracy to below 60m.

AVNIR-2/PRISM Data

Q: Are there already consolidated ALOS products available?

A: No, due to the ongoing calibration campaigns, the data is not consolidated and may contain corrupt datasets.