Multisensor streamer acquisition records both pressure and acceleration in the vertical and crossline directions. It enables the reconstruction of a dealiased representation of the upgoing pressure wavefield at any location within the streamer array. This is achieved by joint reconstruction and deghosting using a generalised matching pursuit (GMP) algorithm. To achieve an independent and quantified evaluation of the reconstruction quality, recorded seismic data is compared with the reconstructed seismic data at a witness streamer location. This paper presents the concept and results of this witness streamer experiment. The results show that mitigations can significantly reduce the impact of the main assumption of the GMP algorithm, which could otherwise compromise the quality of the early-time reconstruction in shallow water. Using these techniques, the reconstruction quality compared with an independent witness streamer is consistent from the shallow part to the deeper part of the data, with a very good match between the recorded and reconstructed data.