What is Bitmask 2112

Post Reply
VPS
Posts: 2
Joined: Fri Jul 12, 2019 1:22 am
company / institution: University of Victoria
Location: Victoria

What is Bitmask 2112

Post by VPS »

Hi Francois,

I have processed my OLCI A Level 1 imageries with the POLYMER-v.4.13 and doing a matchup. Could you please tell me what is bitmask 2112 indicates. I couldn't find any explanation for this particular bitmask in the document. Can we use any pixel with this bitmask?

Also, could you please tell me If the BRDF correction for the POLYMER is applicable only for Case 1 waters?

Best

Vishnu
User avatar
fsteinmetz
Site Admin
Posts: 127
Joined: Fri Sep 07, 2018 1:34 pm
company / institution: Hygeos
Location: Lille, France
Contact:

Re: What is Bitmask 2112

Post by fsteinmetz »

Dear Vishnu,

Bitmask is coded in binary, where each bit represents a flag, as coded in bitmask's attributes, from LAND=1=2^0 to INCONSISTENCY=2048=2^11.
Thus 2112 = 64+2048 = THICK_AEROSOL+INCONSISTENCY
It is recommended to remove pixels where any of the first eleven bits is raised, thus where "bitmask & 1023 != 0" ("&" is the bitwise "and" operator), which is the case for this pixel.

The BRDF correction is applicable to both case 1 and case 2 waters.

Cheers,
François
VPS
Posts: 2
Joined: Fri Jul 12, 2019 1:22 am
company / institution: University of Victoria
Location: Victoria

Re: What is Bitmask 2112

Post by VPS »

Hi Francois,

For the quality control of OLCI A remote sensing reflectance (Rrs), I understood is that the recommended flags to be rejected are all flags with values strictly less than 1024 (the first 10 bits), which does not include CASE2 right? Is that so?

A few of my pixels are raised with Thick Aerosol and Inconsistency flags. Can I keep the inconsistency flags and delete the Aerosol pixel?

Also, I compared the Rrs from POLYMER.410 vs POLYMER4.13 and version 13 shows some instability and whenever the inconsistency flags raised the blue band goes negative and sometimes very weird pattern, like stripes. If you are interested I can send you a ppt where you can see the difference in the spectra.

Best

Vishnu
User avatar
fsteinmetz
Site Admin
Posts: 127
Joined: Fri Sep 07, 2018 1:34 pm
company / institution: Hygeos
Location: Lille, France
Contact:

Re: What is Bitmask 2112

Post by fsteinmetz »

Hi Vishnu,
Indeed, the recommended flags to be rejected are the first 10, which does not include CASE2.
I would advice that you can keep pixels flagged with "INCONSISTENCY" (value 2048) and remove those flagged with "THICK_AEROSOLS" (value 64), but your feedback is welcome if you identified instabilities.
Thanks,
Cheers,
François
Post Reply