b'CommentaryEnvironmental geophysicswith a completely different research goal. This team, based both in Australia (Flinders University) and New Zealand (University of Canterbury and private industry) are interested in groundwater surface water interactions in general, and in particular, in a river system in NewZealand that has been an ongoing study area for some time so is otherwise well-instrumented. In the study reportedon here, they used an Active Distributed Temperature Sensor (A-DTS) setup. In their approach, hot water is used as a tracer to track water motion around the OF. This meant cementing in a copper wire heat source adjacent to the OF string to use as a heat source, so local heat flux could be estimated along Figure 1. RMS amplitude attributes of the time-lapse differences computed at the target horizon for twothe OF string and use that information of the observation wells from the 4D VSP. M6 is the pre-injection survey, M7 shows the results after injectingas a proxy for water velocity, which 4kt, and M8 shows the results after injecting another 12 kt. The black solid contours outline the modeledthen provides information about water plume extent while the black dashed line shows the extent of an earlier injection trial (not discussed here).flux from the losing river system to Modified from Yurikov et al. (2022).the groundwater. They concluded that this approach gave them higher detail information about flux than is available using more conventional methods like differential flow gauging. So, this was not the usual shallow environmental technique or issue that I usually address in this column, but nevertheless is an area of research and data collection that should be of interest to all of us as we work on our ability to image the near surface. Ill be watching this space for sure. ReferencesBanks E. W. et al. 2022. Active distributed temperature sensing to assess surface watergroundwater interaction and river loss in braidedriver systems Journal of Hydrology. 615(12867): 11.Isaenkov R., et al. 2022. Advanced time-lapse processing of continuous DAS VSP Figure 2. Evolution of the CO 2plume captured by the continuous offset VSP monitoring. The colour codedata for plumeevolution monitoring: Stage shows the normalised RMS amplitude of the time-lapse signal at the well/SOV transects. The date and the3 of the CO2CRC Otway project case study. amount of injected gas are displayed for each vintage. The dashed pink contour shows the spatial extents ofInternationalJournal of Greenhouse Gas Control. the earlier plume detected by the 4D surface seismic. The solid pink contours show the extent of the Stage3119 (103716): 17.plume as detected by the multi-well 4D VSP. Note, that for each well/SOV transect, only the area with a time- Pevzner R. et al., 2023. Detection of a CO 2lapse signal (as detected by an interpreter) is displayed. Modified from Isaenkov et al. (2022).plume by time-lapse analysis of Rayleigh-wave amplitudes extracted from downhole DAS recordings of ocean microseisms. The Leading characterise the extent of the injectionby lateral heterogeneity in the area ofEdge. 42 (11): 763-772.was the most ambiguous, with at leastinterest. Interesting nevertheless, as ifSILIXA, Introduction to Distributed Temperature some response in the data attributablethis could be refined, information aboutSensing (July 2020), downloaded from:to the injection event, but with theCO 2movement could be collected withhttps://silixa.com/resources/downloadsconclusion that it was pretty muchno transmitters at all.Yurikov A., et al. 2022. Seismic monitoring of CO 2geosequestration using multi-well 4D DAS impossible to quantify results withOn a different note, it is interesting toVSP: Stage 3 of the CO2CRC Otway project. present understanding of how ocean- look at what Banks et al. (2022) wereInternational Journal of Greenhouse Gas Control. generated Rayleigh waves are affecteddoing with similar equipment, but119 (103726): 12.FEBRUARY 2024PREVIEW 35'