Forum: SARvatore

Epoch and Epoch Reference Gate in GPOD SARvatore/SARINvatore Services Data Products

Dear Users,

Please, be informed this is the correct recipe to retrieve the Epoch ( in seconds or gates) and Epoch Reference Gate in GPOD SARvatore/SARINvatore Services data products:


N_start=N_FFT*over_sampling
N_last=N_FFT*over_sampling+extra_sample*over_sampling*2

    • over_sampling is the zero-padding factor you have applied: if you have applied zero padding, this is 2 , otherwise is 1
    • if you have applied extended window, extra_sample is N_FFT, otherwise is zero

    • N_FFT is 128 for SAR and 512 for SARIN


dt=1/(Bandwidth*over_sampling)

    • Bandwidth is 320e6 Hz for CryoSat-2 and Sentinel-3


time= -dt*(N_start/2) : dt : dt*(N_last-1)/2

    • this is an array from -dt*(N_start/2) to dt*(N_last-1)/2 with step dt


Index=time*(1/dt)

where Index is zero, this is the Epoch reference gate (Epoch_Reference_Gate)


Finally, the epoch in seconds at 20 Hz is:

Epoch_20Hz=Range_Unc_20Hz*2/speedlight-Window_Delay_20Hz

    • Range_Unc_20Hz and Window_Delay_20Hz are fields in the product, speedlight is the speed of the light


Epoch_20Hz in gates is given by:

Epoch_Gates_20Hz=Epoch_20Hz* Bandwidth *over_sampling +Epoch_Reference_Gate


Salvatore Dinardo



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