Stake-Less Nodal Seismic Deployment Using Internal GNSS Receiver

Abstract Pre-surveying receiver point locations is extremely time consuming and unreasonably lengthen seismic acquisition projects if the planned receiver grid is very dense. An alternative is to approximately deploy receivers and then use receivers internal Global Navigation Satellite Systems (GNSS) device for their final position. After some cleaning, these positions have an acceptable accuracy to be used in the processing of the seismic data. Receiver deployment does not need accuracy. In practice it was carried out using a hand-held GNSS device, but it could have been done using simpler techniques like line of sight or steps counting. On the contrary, final positions need accuracy so that processing tools work optimally. While one GNSS measurement is not precise enough, repeated measurements at the same position are refined and combined into a much more accurate final position. Accuracy obtained following this procedure is below three meters in most cases, thus acceptable for all seismic processing algorithms. Tests performed on real seismic datasets show that perturbations of less than six meters for receiver positions does not adversely impact the seismic image quality. Based on these findings, it was decided to make use of GNSS-derived horizontal coordinates. The accuracy of these coordinates, taken individually, is low but by combining several days of GNSS readings, the accuracy can reach acceptable levels, to below three meters. Since geophone nodes are usually deployed to the same location for several days or even weeks, large numbers of GNSS readings are available to be processed into a single accurate position. Raw GNSS vertical coordinates are even less accurate than horizontal ones and cannot been improved adequately. Instead, a Light Detection and Ranging (LiDAR) survey over the entire seismic survey area, provided centimeter accuracy for nodal geophones' elevations. Such LiDAR survey does not need to be concomitant to the seismic survey and thus does not hamper the seismic survey schedule. Modern land seismic nodal systems onboard GNSS receivers. While GNSS receivers are primarily used in nodes to define times for recorded seismic traces, they can also provide horizontal coordinates of an acceptable precision simplifying greatly node layout and removing the need for lengthy and costly surveying operations.