code: def _find_navigation_coefs(self):
          
          # Find index of interval enclosing the nominal timestamp of the scan
          time = np.datetime64(self.prologue['ImageAcquisition']['PlannedAcquisitionTime']['TrueRepeatCycleStart'])
          intervals_tstart = self.prologue['SatelliteStatus']['Orbit']['OrbitPolynomial']['StartTime'][0].astype(
              'datetime64[us]')
          intervals_tend = self.prologue['SatelliteStatus']['Orbit']['OrbitPolynomial']['EndTime'][0].astype(
              'datetime64[us]')
          try:
              return np.where(np.logical_and(time >= intervals_tstart, time < intervals_tend))[0][0]
          except IndexError:
              raise NoValidNavigationCoefs('Unable to find navigation coefficients valid for {}'.format(time))
docs: Find navigation coefficients for the current time
  
          The navigation Chebyshev coefficients are only valid for a certain time interval. The header entry
          SatelliteStatus/Orbit/OrbitPolynomial contains multiple coefficients for multiple time intervals. Find the
          coefficients which are valid for the nominal timestamp of the scan.
  
          Returns: Corresponding index in the coefficient list.