Page 1 of 1

How to interpret the latitude and longitude vertice information in OCO data

Posted: Thu Aug 19, 2021 5:00 pm America/New_York
I'm working with OCO-3 Level 2 CO2 data.

The field "/RetrievalGeometry/retrieval_vertex_latitude" is described in the user guide as "the latitude at each of the corners of the parallelogram that defines the field-of-view."

I'd expect this field to thus contain 4 data points, one for each corner of a parallelogram. However, the field contains as 4 x 3 table for each sounding. I'm unsure where the field-of-view is contained in the data.

Any guidance is appreciated.

Re: How to interpret the latitude and longitude vertice information in OCO data

Posted: Fri Aug 20, 2021 3:44 pm America/New_York
The dimension size 3 correspond to the three bands of the OCO
instrument (O2, WeakCO2,StrongCO2)
The vertices are given for extra information purposes, to give a sense where
the three radiometers were looking for the particular sounding. If you plot the
three polygons per sounding, you should see they are very close. This can also
be affirmed by checking the "retrieval_center_offsetâ€¦" arrays - you should see
values like 50-80 meters. Technically you can use the vertices for advanced
plotting of the final retrieval, but note that the latter is a combined result
of inversion in the three bands, and thus doesn't have band dimension. Hence,
you could plot the soundings as polygons, by either choosing any band vertices,
say, the O2 vertices, or, more complex, calculating a "middle" polygon by
finding the middle vector to each of the vertices.
In the simplest case, you just use the center or the retrieval FOV,
"retrieval_longitude" and "retrieval_latitude".

Re: How to interpret the latitude and longitude vertice information in OCO data

Posted: Mon Aug 23, 2021 7:25 am America/New_York
Great! This is the perfect guide I need for my WAEC Students that I'm tutoring the this year's WASSCE Exams. Hopefully, they will make a great result this year. Thanks, earth data for this information.