Satellite images or airborne images can indicate groundwater potential but present different levels of uncertainty. For example, in the case of fractured-rock aquifers, we know that detecting lineaments (fractured-rock structural features that can be observed from above in the landscape) can help in identifying zones with faults associated with a dense fracture network that are favorable to groundwater flow. However, the level of accuracy of such observations is very low considering that the scale of a preferential flow zone associated with a fault is very narrow (a few meters apart from the faults). Very few studies have been interested in looking at the issue of the accuracy of satellite images for determining groundwater potential; this is a relevant issue.

https://visibleearth.nasa.gov/view.php?id=79184

Article Beyond GRACE: Using Satellite Data for Groundwater Investigations

In general, remote sensing from satellites would give substantial uncertainty. However, highly experienced geologists, hydrogeologists have learned to read the ground and topographic features, the scarps, earth flows, lineaments, stream morphology, vegetation and other indicators. So they are apt to see things that the average analyst may not. However, most would core geology and soils to look for groundwater and hydric soil features, identify aquifer depths and boundaries, conduct samples, run hydraulic conductivity tests, etc. I had a great uncle in western Nebraska, who was known to have a gift in water divining, not only locating but estimating quantity of water with a forked willow cutting as I remember him describing his gift to me.

In Oregon, Geologist Joe Cornell showed me how to locate underground flow network using bent metal welding rods. It appeared to work in a few instances. We used it to locate underground flow pattern in potentially unstable, landslide prone terrain when locating possible routes for log or access roads. There is much unknown about the subject of remote sensing of groundwater, but some are more experienced or gifted than others.

However, confirmation comes from coring and sampling, digging and or instrumenting wells for water level, various well pumping tests, obtaining records from other wells, water levels in streams, lakes, ponds, etc., extent of hydric vegetation, maps of topography, any information on aquifer(s) character and depths, etc.

Even with my interest in your subject, I have not taken steps to explore it myself. I am doubtful that obtaining satellite images, even under various color schemes, would tell me much. Granted, infrared photos or images tends to differentiate some surface moisture gradients and bottomland hardwoods from upland species, but the conditions in subsurface confined aquifers can be significantly different from surface indicators. Your mention of experts may be the key. Unfortunately, I do not know any scientists, geologists, well drillers who have relied on this approach. I would welcome opportunity to learn more, but if you can, learn from them (experts), try their methods, verify that they work for your circumstances. If they are relying on satellite indicators, at some points in time, they have also used the ground truthing methods and sampling to confirm and validate their interpretations. They should be able to estimate the level of certainty or uncertainty, and this might vary with conditions.

William F. Hansen

You said it well. Thank you so much for your explanation. I strongly agree with you. Experience really matters. But, as you mentioned it well, quantifying the levels of certainty/uncertainty is also very important.

Satellite imagaries are the beginning in hydrogeological exploration. They indicate the groundwater potential areas in the light of topography, rock type, rock structure like folds, faults, shears, joints and fractures ;normally reflected as linear features or lineaments. These rock structures are likely to store and transmit ground water. Field study is always essential to confirm the indications. Essentially good knowledge of the geology of the area is required. Singularly satellite images help to limit our focus to the potential areas only thereby reducing time for elaborate field work.

One thing to remember that the satellite imagaries are prepared on the basis of about 10 % ground truthing.

In general, remote sensing from satellites would give substantial uncertainty.

Groundwater exploration is more effective if it combines different scales of observation (rock sample, outcrop, watershed). It cannot therefore be reduced to the study of satellite images, but these are an interesting tool for "scaling up" the results derived from observations made at a smaller scale.

In arid areas (with little vegetation), we use free images (such as those published on Google Earth) as an economic tool for rapid geological mapping and therefore for defining the geometry of reservoirs that have been confirmed through preliminary boreholes. Under dense forest cover (in equatorial areas), this exercise is much more difficult.

In crystalline basement areas, satellite images have replaced aerial photos that were previously used for lineament identification (which often mark fracture zones).

Satellite images are useful on a large scale. In small scale study one needs to see a satellite image on a smaller scale, say 1: 10000 or smaller. Study of a top sheet in 1: 50000 or 1: 25000 scale is also very usefully. However interpreting the remote sensing data in the light of the geology and hydrogeology of the area is the key (!) In absense of which satellite images would be utterly confusing and misleading. I have seen persons without any knowledge of geology or hydrogeology using satellite imagaries in 1: 50000 scale for locating bore well sites simply because they saw locations with intersection of several lineaments only and found dry bores on this basis!

Naba Kumar Shukla

I like your explanation. But, I have one more question for and may be for others as well:

Is it only for lineament extraction purposes that we need satellite images in groundwater exploration works?

Following answers.....

I like Dr. Shukla's comments - a lot can be learned from satellite imagery, but it needs to be corroborated with other mapping and ground truthing.

Satellite imagaries are useful in interpreting the topography, soil type and soil moisture, drainage characteristics apart from lineament identification, which aid in hydrogeological investigation. No doubt satellite imagaries are very useful tool in hydrogeological investigation. They are also used in forestry, oceanography, agriculture and many other fields. As interpretation technique varies for different uses.

Satellite images assist with planning geophysical profiles which give more information about the depth, orientation as well as degree of weathering of structures and contact zones.

It also provides insight into regional lineaments orientation.

Best groundwater exploration is exploration drilling following a desktop assessment (which will include a water balance) and geophysical survey etc. Basically calibrating the geological maps and geophysics again to the drill log.

Also an aquifer can potentially be ideal, but without rainfall or other replenishing resource, no water can be sustainable abstracted at economical volumes. Hence artificial recharge and transboundary recharge methods are increasing in some areas - to take advantage of having a 'dam' underground but make up for the lack of rainfall in that area. Hence satellite imagery mostly only speak to the geology, and the lineaments with which groundwater is more probable and associated - but not to whether groundwater actually is available. That only a drill bit can do.

My 2c.

Satellite images can provide much more than just geological context illustration. Suitable use of high resolution images can be used to estimate groundwater table depth in marsj areas (Bechtold M, Schlaffer S, Tiemeyer B, De Lannoy G (2018) Inferring Water Table Depth Dynamics from ENVISAT-ASAR over a range of Peatlands from deeply drained to natural conditions. Remote Sens., 10(4), 536, DOI 10.3390/rs10040536) or in arid environment where cattle is used to extract groundwater (Collignon B. & Mohamed Vall M.M. 2022. Remote sensing exploration of piezometric depressions in the Taoudeni basin (Mali-Mauritania). Arabian J.Geosciences. doi 10.1007/s12517-022-10552-1).

@Cindy. I agree with you fully. After all remote sensing is only an indirect tool for planning. Much more remains to be done subsequently for substantiation.