Ashish Joshi, Suresh Kannaujiya, Shefali Agarwal, R. S. Chatterjee and R. P. Singh

Submarine groundwater discharge (SGD) is the flow of groundwater from land to sea that occurs in the sub-surface. Groundwater seeps from the surface through aquifers and when the water level in the aquifer is higher than sea level, the water flows into the ocean. SGD can occur as seepage or submarine springs. The flow of fresh and saline groundwater into the ocean has been revealed by studying nutrients and radioactive elements from land to ocean. There are various ground-based techniques for the detection of SGD but thermal remote sensing can provide significant information for SGD analysis. The change in temperature of seawater due to the formation of SGD forms the basic principle of its detection from remote sensing. There are Spaceborne thermal infrared imaging instruments in the satellites like LANDSAT, ASTER, MODIS, ECOSTRESS etc. which are useful for studying heat-related phenomena on the Earth’s Surface. The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) was launched to the International Space Station (ISS) in 2018 and has as its primary mission for the identification of plant thresholds for water use and water stress. The instrument is also useful for studying heat-related phenomena, like patterns of heat absorption for several applications. It provides the Radiance, geolocation, land surface temperature, emissivity, and cloud products (level 1 and 2 products). There is a total of 6 bands in which 5 spectral bands are in the 8-12.5 μm range and one band at 1.6 um for geolocation and cloud detection. ECOSTRESS will observe the same spot on Earth at different times each day due to the unique orbit of the ISS.The level-2 tiled products provide the land surface temperature at 70 m resolution.

Figure 1: a) Landsat (FCC) Image of 08 Dec 2024 b) ECOSTRESS Thermal Infrared image of 10 Dec. 2024 of Okha Coast, Gujarat, draped over FCC image

Okha region of Gujarat has many geo-hydrological features such as the availability of sufficient rainfall, limestone rocks, and less drainage density which are favourable for the SGD process. ECOSTRESS level-2 data of the Okha region has been analysed for studying the SGD for the month of December 2024. The figure 1(b) shows the ECOSTRESS land surface product overlaid on the False Color Composite (FCC) of the Okha region. The figure 1(b) clearly shows the SGD signal in the bluish colour due to the localized low-temperature region on the western side of Okha Coast. The study shows the potential of spaceborne thermal infrared sensor for the detection of SGD from space and can be helpful for the ISRO upcoming satellite mission like  TRISHNA (Thermal Infra-Red Imaging Satellite for High-resolution Natural Resource Assessment).

References

Singh, R.P. et al. (2020), Identification of Submarine Groundwater Discharge using Thermal Infrared Observations in Arabian Ocean near Okha Coast, Gujarat. India. Current Science, 119(9), 1558-1564.

Selvam, S. et al., (2020), Quantification of submarine groundwater discharge (SGD) using radon, radium tracers, and nutrient inputs in Punnakayal, south coast of India. Geosci. Front., 2020; https:// doi.org/10.1016/j.gsf.2020.06.012

Sekar, S., Perumal, M., Roy, P.D. et al. (2022). A review on global status of fresh and saline groundwater discharge into the ocean. Environ Monit Assess 194, 915 https://doi.org/10.1007/s10661-022-10566-y

https://ecostress.jpl.nasa.gov/instrument