The value adopted by IAG is 62636853.4 m^2/s^2. 

Article A conventional value for the geoid reference potential W_0

Dear Abdel Rahim, methods of estimating the geoid geopotential value W0, in addition to the previous and recent estimates have been described in some details in our paper "A conventional value for the geoid reference potential W0, doi:10.1007/s00190-016-0913-x" . This paper would satisfy your question. Nadim

Hi Abdel Rahim, I agree with the value quoted by Mustafa (above) and have appended Laura Sanchez et al which outlines the approach taken and justification for getting this value. However, I understand the US NGS still uses the 1999 value of xxx 856.0 for its newer geoid/height datum. It shouldn't be much a problem transforming from one to the other as its basically a datum shift or bias in the geoid heights. Bill Kearsley

Hi ,ALL

Thank you very much for all

Special thanks to Dr.Nadim,Mustafa

 and Prof. Kearsley

Regards

Abdel Rahim