Accurate velocity models that include long-wavelength components are required for precise subsurface structure imaging and estimation of geophysical properties. To successfully build the long-wavelength velocity using full waveform inversion (FWI), sufficient offset and low-frequency components are necessary. However, due to the limited acquisition conditions, it is difficult to operate long offset and low-frequency sources in coastal shallow marine. Short offset makes the data dominated by reflections, and FWI intensively updates the surface boundaries. Although reflection full waveform inversion (RFWI) has been proposed to reconstruct long-wavelength velocity models using reflection data, it suffers from cycle skipping when low-frequency component is insufficient. To overcome these limitations, we propose a direct envelope-based RFWI (DE-RFWI) that incorporates the direct envelope into the RFWI. By employing envelope-based energy information from reflection data, DE-RFWI facilitates the reconstruction of long-wavelength velocity. The proposed method employs the Hilbert transform-based implicit gradient decomposition technique to address additional computational cost. To verify the proposed method, DE-RFWI was applied to synthetic test with a shallow marine condition and field data acquired in Yeongil Bay, South Korea. The inversion results for field data were evaluated by analyzing arrival-time alignment in envelope domain. The results demonstrate that DE-RFWI can reliably reconstruct long-wavelength velocity models in shallow marine seismic data and improve reflector continuity and resolution in the reverse time migration imaging.