Rayleigh optical thickness for airborne sensors

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yang16
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Joined: Wed Mar 30, 2016 8:28 am America/New_York

Rayleigh optical thickness for airborne sensors

by yang16 » Fri Jun 18, 2021 5:30 am America/New_York

Dear EARTHDATA Forumn,

I learned that NASA Ocean Color provides Rayleigh optical thickness for satellite sensors (VIIRS, SeaWiFS and MODIS) at different bands. My question is that is it possible to interpolate the Rayleigh optical thickness from a satellite altitude to an airborne sensor altitude, for example the CASI-1500 sensor with an altitude of 2 km? Or do you know how to calculate the Rayleigh optical thickness for the CASI-1500 sensor?

Thanks,
Mengmeng.

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OB.DAAC - SeanBailey
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Re: Rayleigh optical thickness for airborne sensors

by OB.DAAC - SeanBailey » Mon Jun 21, 2021 9:07 am America/New_York

The estimates of top-of-atmosphere Rayleigh radiance in the processing of satellite-based ocean color sensors requires radiative transfer simulations that account for the spectral bandpass of the sensor and an estimate of the surface component as modulated by a roughened ocean (using windspeed to derive surface roughness). The l2gen code can process data from the AVIRIS airborne instrument, bu only in an experimental manner (i.e. not fully supported). To account for the altitude of the aircraft, we adjust the Rayleigh radiance for AVIRIS using a very simple assumption:

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scaleRayleigh = 1.0 - exp(-l1rec->alt / 10); // Assume 10km is e-folding height
AVIRIS flies on the ER-2, at ~ 20km, so a bit higher up than the 2km for the CASI-1500 sensor data you have, so this simple assumption may not be sufficient for your needs.

Other groups have processed aircraft-based ocean radiometers (i.e. Naval Research Laboratory) and have developed data processors that can account for varying aircraft heights (e.g. TAFKAA, 6S). These may be more adaptable to your needs.

Regards,
Sean

yang16
Posts: 17
Joined: Wed Mar 30, 2016 8:28 am America/New_York

Re: Rayleigh optical thickness for airborne sensors

by yang16 » Tue Jun 22, 2021 4:18 am America/New_York

Hi Sean,

Thank you very much for your detail reply. It helps a lot.

Kind regards,
Mengmeng.

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