[Py6S] Create Diffuse SkyLight Look-Up-Table (LUT)

[Sheng-ye Jin]

Hi Robin and all,

I would like to retrieve surface albedo from a sensor image. Therefore, I am trying to determine diffuse skylight fractions by interpolating from a Diffuse Skylight LUT. 

My question is: 

Is that possible to create such a LUT like the LUT below by using 6S/Py6S model?

Example of LUT:

Aerosol_type: Continental <-- input aerosol type

MODIS_Band_1: (0.620,0.670) < -- input wavelength range

S&O| 0.00   0.02   0.04  0.06   0.08   0.10 ...  0.94   0.96   0.98   <---Total atmosphere Optical thickness (O), 

_____________________________________________________________ 

 0    |0.029 0.042 0.055 0.067 0.079 0.091 ... 0.465 0.472 0.478 

 1    |0.029 0.042 0.055 0.067 0.079 0.091 ... 0.465 0.472 0.478 

 2    |0.029 0.042 0.055 0.067 0.079 0.091 ... 0.465 0.472 0.478 

 3    |0.029 0.042 0.055 0.067 0.079 0.091 ... 0.465 0.472 0.478 

 4    |0.029 0.042 0.055 0.067 0.079 0.092 ... 0.466 0.472 0.479 

 5    |0.029 0.042 0.055 0.067 0.080 0.092 ... 0.466 0.473 0.479 

 6    |0.029 0.042 0.055 0.067 0.080 0.092 ... 0.467 0.473 0.479 

.      |

.      |

.      |

.      |

89   |0.895 0.957 0.983 0.993 0.997 0.999 ... 1.000 1.000 1.000 

90   | 0.00 0.000 0.000 0.000 0.000 0.000 ... 0.000 0.000 0.000

^

solar incident zenith

O = aerosol.depth.at550nm(visability=20km) + molecular_depth(wavelength)

Thanks and look forward to your advice.

Jin

-----------------------------------------------------------------------------

SHENG-YE JIN (PH. D.)

Environmental Informatics Laboratory

Department of Civil and Earth Resources Engineering, 

Kyoto University Graduate School of Engineering

C1-1-209, Kyoto-daigaku katsura, Nishi-kyo ku, Kyoto, 

615-8540, Japan

E-mail: shengye.j(at)gmail.com

            jin.shengye.2r(at)kyoto-u.ac.jp

Tel / Fax:   +81 – 075  –  383 – 3302

 iPhone :    +81 – 080 – 4828 – 4291

[Robin Wilson]

Hi,

Sorry for the slow reply on this, I've been away a lot recently.

This should be possible in Py6S. You can create a LUT by looping over all of the various variables and storing the outputs (the itertools.product from the Python standard library is useful for this - see https://docs.python.org/2/library/itertools.html#itertools.product).

In terms of setting the parameters:

1. You can set the aerosol type (https://py6s.readthedocs.io/en/latest/params.html#Py6S.AeroProfile.PredefinedType)

2. You can use MODIS bands (https://py6s.readthedocs.io/en/latest/params.html#Py6S.Wavelength)

3. You can get the total optical thickness as s.outputs.optical_depth_total

4. You can get aerosol optical depth by calculating it from the aerosol scattering transmittance (s.outputs.transmittance_aerosol_scattering.downward), as optical_depth = -ln(transmittance) (ie. -1 * the natural logarithm of transmittance).

5. You can get the Rayleigh scattering optical depth (which is what I assume you mean by the molecular depth) by calculating it as above, but using s.outputs.transmittance_rayleigh_scattering.downward.

I think that covers everything,

Robin

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