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Topic Products and Algorithms / Satellite Data Products & Algorithms / regarding use in situ data comparison (locked)
I received the following question from a user and permission to post it on the Forum. I have already provided a brief description of the OC4 nLw radiance ratio algorithm used to calculate chlorophyll concentration, but the question regarding the in situ data is interesting and the answer may be useful to other researchers.
"I'm doing work with chlorophyll-a concentration in Bay of Lisbon with SeaWIFS images anda in situ data.
I don't know how the chlorophyll-a is 'viewed' by the sensor. How does the sensor measure the chlorophyll-a concentration?
Can you help me?
What should I do with the in situ data?
a) Integrated (all values of chlorophyll-a ) in the whole water column?
b) Integrated (all values of chlorophyll-a ) since the top to k^-1 level ?
c) The mean valuea of chlorophyll-a since the top (z=0) to k^-1 level?
d) or follow the Smith equation (1981), where I have to count with the ''weigting funcion'' ( g(z)= exp (-2k.z))
where k^-1 = k490"
Thanks for help with this question.
"I'm doing work with chlorophyll-a concentration in Bay of Lisbon with SeaWIFS images anda in situ data.
I don't know how the chlorophyll-a is 'viewed' by the sensor. How does the sensor measure the chlorophyll-a concentration?
Can you help me?
What should I do with the in situ data?
a) Integrated (all values of chlorophyll-a ) in the whole water column?
b) Integrated (all values of chlorophyll-a ) since the top to k^-1 level ?
c) The mean valuea of chlorophyll-a since the top (z=0) to k^-1 level?
d) or follow the Smith equation (1981), where I have to count with the ''weigting funcion'' ( g(z)= exp (-2k.z))
where k^-1 = k490"
Thanks for help with this question.
Currently, [chl] is estimated using an empirical relationship that relates ratios of satellite radiances (in particular, remote-sensing reflectance) to [chl]. These relationships are described in detail in number of manuscripts, but you might start with:
Gordon et al. (1983), Appl. Optics, 22, 20-36
O'Reilly et al. (1998), J. Geophys. Res., 103, 24937-24953
O'Reilly et al. (2000), SeaWiFS Postlaunch Technical Report Vol. 11
The latter is located online at:
http://oceancolor.gsfc.nasa.gov/cgi/postlaunch_tech_memo.pl?11
In general, the optically-relevant constituents in the water column from the surface to the depth of the 10% light level (z90) all "contribute" to the water-leaving radiances observed by the satellite. As such, for our validation exercises, all in situ [chl] from z(0) to z90 are considered. Currently, these observations are weighted using methods similar to that of Gordon and Clark 1980 (Appl. Optics, 19, 3428-3430) and Smith 1981 (MEPS, 5, 359-361) -- as you mentioned in example d.
Hope this helps. Best regards.
Gordon et al. (1983), Appl. Optics, 22, 20-36
O'Reilly et al. (1998), J. Geophys. Res., 103, 24937-24953
O'Reilly et al. (2000), SeaWiFS Postlaunch Technical Report Vol. 11
The latter is located online at:
http://oceancolor.gsfc.nasa.gov/cgi/postlaunch_tech_memo.pl?11
In general, the optically-relevant constituents in the water column from the surface to the depth of the 10% light level (z90) all "contribute" to the water-leaving radiances observed by the satellite. As such, for our validation exercises, all in situ [chl] from z(0) to z90 are considered. Currently, these observations are weighted using methods similar to that of Gordon and Clark 1980 (Appl. Optics, 19, 3428-3430) and Smith 1981 (MEPS, 5, 359-361) -- as you mentioned in example d.
Hope this helps. Best regards.
Topic Products and Algorithms / Satellite Data Products & Algorithms / regarding use in situ data comparison (locked)