Dear Akash! I have attached a exoatmospheric values for Landsat 8. I hope that will help you. 

Thank you dear jahangir, but I need the ESUN value of band 1 of Landsat 8

You may want to look at the attached link for description on ESUN values of OLI. Are you aware that you can now directly get atmospherically corrected L8 OLI data from USGS?

https://landsat.usgs.gov/where-can-i-find-solar-exoatmospheric-spectral-irradiances-esun-values-landsat-8-oli-data

Jahangir Khan,

Is there any reference to this table?

James Varghese ,

The link does not open. Could you please provide an updated link?

Dear if you tack a look to the Landsat 8 guide you will fin all equatios that you need to retrieve mean solar exo- atmospheric irradiance(ESUN) from a Landsat 8 image

Kriti Mukherjee, the USGS link that I attached with my previous comment works just fine. Not sure why you can't open it. May be I can quote the main contents of the link here in italics:

Question:

Where can I find the solar exoatmospheric spectral irradiances (ESUN) values for Landsat 8 OLI data?

Answer:

ESUN values are not provided for Landsat 8 data because they are not required for converting data to reflectance. Landsat 8’s Operational Land Imager (OLI) adopted two independent National Institute for Standards and Technology (NIST) traceable radiance and reflectance calibration methods. The Landsat 8 metadata file provides coefficients necessary to convert to radiance and reflectance from the quantized and calibrated Digital Numbers (DNs) of the product. Thus, ESUN values are not required for reflectance conversion.

Relative Spectral Response (RSR) of the OLI spectral bands can be used along with the user’s preferred solar spectrum to calculate ESUN values corresponding to Landsat 8 OLI bands. (NOTE: ESUN values calculated from RSRs were not used for OLI calibration).

Additional links:

http://landsat.gsfc.nasa.gov/?p=5779

https://landsat.usgs.gov/using-usgs-landsat-8-product

James Varghese ,

Thank you very much. I was confused because I was trying to compare the results with the TOA product the Google Earth Engine uses ( LANDSAT/LC08/C01/T1_TOA ) and there the reference is cited as Article Summary of current radiometric calibration coefficients for ...

The paper does not include the conversion for Landsat 8, and I was therefore following the steps as mentioned for Landsat 7.

From your link, however, it appears that we don't need the ESUN for converting to TOA reflectance. Please let me know if you have any other information regarding this.

Kriti Mukherjee, I think the use of ESUN really depends on your research application, i.e., whether you are trying to compare two (with and without ESUN) different calibration methods or some other research purpose. As stated in the official source (USGS) they do not use the ESUN for Landsat 8. However, you will find examples on the web where ESUN values of L8 were derived. I've attached an example link that I found which shows how ESUN values were derived for L8 OLI through the R package RStoolbox.

http://bleutner.github.io/RStoolbox/r/2016/01/26/estimating-landsat-8-esun-values

James Varghese

Thank you. Yes, I had seen this and therefore asked for the reference to the values mentioned by Jahangir Khan. Anyway, thanks a lot for the information you shared. It was very helpful.

Does any one knows how to get InSAR images of Pakistan?