# ResourceSat-2 LISS-4

ResourceSat-2 LISS-4 acquisitions are calibrated using the Orfeo Toolbox.

ISRO provides the formula below to convert the DN into radiance:

$L_{(b)} = { {DN \times SR_{(b)} } \over 1024}$

Where:

• $$SR_{(b)}$$ denotes the Saturation Radiance and these values (mW/(cm2-sr-um) are for LISS-4:
 Common band name Band SR green B2 47.5614 red B3 45.6990 nir B4 31.5000

For the conversion from $$DN$$ (for Digital Numbers) to spectral radiance (or ‘TOA radiance’) $$L$$, the following formula is used :

$L_\lambda = gain \times DN + offset$

As such, the calibration uses:

$gain_{(b)} = {SR_{(b)} \over 1024}$

and

$offset_{(b)} = 0$

$$L$$ in $$W/m^2/steradians/micrometers$$ with $$b$$ being a band ID.

To convert TOA radiance to TOA reflectance, the following formula is used :

$R(b) = { {\pi \times L(b) \times d \times d} \over {ESUN(b) \times cos(θ)} }$

where :

• $$L(b)$$ is the spectral radiance for band b

• $$pi$$ is the famous mathematical constant

• $$d$$ is the earth-sun distance (in astronomical units) and depends on the acquisition’s day and month

• $$ESUN(b)$$ is the mean TOA solar irradiance (or solar illumination) in $$W/m^2/micrometers$$

• $$θ$$ is the solar zenith angle in degrees.

The values for the $$ESUN(b)$$ for LISS-4 are provided in the table below:

 Common band name Band Mean TOA solar irradiance green B2 181.89 red B3 156.96 nir B4 110.48

## Input

The input is an ingested ResourceSat-2 LISS-4, see details here.

## Output

The output is a STAC item geojson ... including the assets ...