FAQ
Albedo and BRDF

Q: What happens when the weighted number of samples is less than 1?
A: Data used is background prior

TIP-BHR-LAI/FAPAR

Q: What is the size of the full 0.05 degree daily BHR-TIP LAI/FAPAR dataset?
A: About 1 TB.

Q: What is the size of the full 0.5 degree daily BHR-TIP LAI/FAPAR dataset?
A: About 15 GB.

Q: What do the retrieval_flag values in the BHR-TIP LAI/FAPAR product mean?
A: They contain important quality and processing information and should not be ignored. Please check the Product User Guide for details.

Q: What is the meaning of the value 0x740 in the legend of the BHR-TIP LAI/FAPAR animation's quality panel?
A: It is a hexadecimal number summarising the flag values which have been used for filtering the data for the "dubious" set. These are: tip_untrusted, obs_inconsistent, obs_nosnow_hinunc, and obs_snow_hinunc. Please check the Product User Guide for details.

Q: What is the meaning of the "1-sigma rel. unc." panel in the BHR-TIP LAI/FAPAR animations?
A: It gives an overview of the uncertainty estimate for the data without warning flags ("good" data). The value shown is the 1-sigma uncertainty divided by the retrieved values in percent, hence "1-sigma relative uncertainty".

Q: What is the meaning of "surface state" panel in the BHR-TIP LAI/FAPAR animations?
A: TIP uses two different sets of priors, one for snow-covered ground surface and one for snow-free ground surface. This panel shows which prior set was used. In the "mixed" case both sets are used and the result is a weighted average, based on the temporal distance of the respective snowy and snow-free albedo observations. Refer to the Algorithm Theoretical Basis Document for details.

Q: Which retrieval_flag values should I use for masking out data?
A: A conservative choice is: tip_untrusted, obs_inconsistent, obs_nosnow_hinunc, and obs_snow_hinunc (0x740), as used for the animation's quality panel. Please check the Product User Guide for details.

Q: Why is BHR-TIP LAI "effective"?
A: It is the model parameter of the two-stream model controlling the amount of leaf area per ground surface area in an idealized representation of the canopy, using very small lambertian scatterers for leafs, as in a turbid medium. It is related to the actual LAI through a canopy dependent structure factor.

Q: Is BHR-TIP fAPAR also "effective"?
A: No, it is just the best guess about the partitioning of the fluxes in the canopy, based on the assumptions of the two-stream model and its priors.

Q: I see jumps in the TIP products, which are not present in the albedos. What can be the cause?
A: There are two possibilities: (1) A different table based on a higher or lower albedo uncertainty was used. This can be checked looking at the retrieval_flag which documents the tables used. These jumps are relatively small. (2) A very different two-stream inversion is more probable for only slightly different albedos. There is no dedicated marker for this, but it typically happens around certain values, simultaneously for FAPAR and LAI (FAPAR from ~0.5 to ~0.7 and back, LAI from ~1 to ~3-4 and back), with visible band albedo less than ~0.11.