How to correctly parse MODIS QA layers?

[modis_user]

Hello,

 

I'm currently working with the MODIS product MOD13Q1 (Vegetation Indices 16-Day L3 Global 250m) and I ran into some difficulties with the interpretation of the quality assessment information. I already posted my question on stackexchange ( http://gis.stackexchange.com/questions/171792/how-to-correctly-parse-modis-qa-layers ), but got no answers. Maybe anybody here has an idea?

 

If I receive an answer here, I will update the question on stackexchange (and vice-versa). 

 

Here's the text of the question (identical to stackexchange):

 

I'd like to correctly parse the MOD13Q1 VI Quality layer (see Table 2 in "layers" here). For this, I'm trying to follow Example 1 from this tutorial (page 10).

I'll illustrate my problem with a pixel value of "VI Quality" from my real data set: 35038

First, I transform it to the binary value 1000100011011110.

Then, I separate this binary value into different bit words (from right to left) according to Table 2:

1 0 001 0 0 0 11 0111 10

Following Example 1 ("Please bear in mind that the binary bit-string is parsed from right to left, and the individual bits within a bit-word are read from left to right."), I would then assume that I'd get the following bit words for the different categories:

 

MODLAND_QA: 10
VI usefulness: 0111
Aerosol quantity: 11
... and so on

 

However, the problem is that the value 0111 doesn't exist in Table 2. I guess that there are two possible explanations for this:

1. I made a mistake trying to apply the tutorial. In that case I'd be very thankful if somebody could point me to the right direction.
2. I applied the tutorial correctly, but Table 2 is incorrect or incomplete. Could anybody confirm if this might really be the case, and if yes, where to find information about missing values?