With high resolution DTMs (say, 1-5m) it might be possible to highlight differences in elevation when two grids are available (one referring to the past and one more recent) through their algebric difference.

If changes are very small the vertical error of grids might create problems as it could be larger than the real difference due to subsidence, thus bringing to 'spurious' changes in elevation. Anyway in some cases the difference raster can give an overall idea of what is happening.

Subsidence of peat is in my experience much slower than can be detected by recent sequential DEMs. Even the cm accuracy of laser will be of no help here for the same reason. Your best bet could be historical water level measurements of the farmland on lowland peat in the western Netherlands formerly cropped, but currently grassland because of subsidence over the centuries due to drainage.

I very much doubt that peatland thickness could be measured by RS. This is the same question as if one can measure the thickness of a geological layer. Am I wrong?

Accurate measurement of peat layer thickness by RS is not possible, even use of groundpenetrating radar gives only approximate overview of the situation.

Use of high resolution sequential DEMs can be used but only in specific cases - if you have pre-drainage DEM and DEM of several years (better decade) after drainage. And even then this works only if the initial peat bulk density is low (e.g. Sphagnum peat) and surface is not densely covered by shrub or other higher vegetation. In case of high bulk density the subsidience is very slow process and error due to vegetation cover  is bigger than detected  subsidience. In general, airborne LIDAR measurements can be used but not satellite data (unless more sophisticated approach with SAR is used).

Peat thickness: not possible with remote sensing. Radar, whether it is satellite based or ground based, will not pass through the groundwater table, no matter if you choose the longest wavelength available. For measuring subsidence, SAR interferometry can be used to achieve centiometer accuracy. See for example studies  on the North coast of Java, Indonesia:

Chaussard, E.; Amelung, F.; Abidin, H.; Hong, S.H. Sinking cities in Indonesia: ALOS PALSAR detects rapid subsidence due to groundwater and gas extraction. Remote Sens. Environ. 2013, 128, 150–161.

Lubis, A.M.; Sato, T.; Tomiyama, N.; Isezaki, N.; Yamanokuchi, T. Ground subsidence in Semarang-Indonesia investigated by ALOS–PALSAR satellite SAR interferometry. J. Asian Earth Sci. 2011, 40, 1079–1088.

With the TerraSAR-X, measurements of land subsidence should be even more precise than with the ALO PALSAR, because of its shorter wavelength.

Dear Jens Oldeland, Ain Kull, Wietske Bijker, Marco Barbujani, Hein Van Gils, I appreciate your answer. I also think that, it is almost impossible using RS to measure the peat soil thickness. It is a need to combine RS with ground truth, including georadar, electrical resistivity image (ERI), and hand boring. Thank you for your kind attention  

Dear Ari Sandhyavitri, you are welcome, good luck for your researches.

Dear Ari,

For experience, the best representation of peat thickness is using manual probing. Of course you can have some errors but it is better than any remote sensing technique. However, it is time consuming.

One could use digital photogrammetry, using top-view imagery collected with e.g. UAV or camera-on-stick when interested in a single peatland. Remote sensing (e.g. InSAR) has had some great developments recently, but will require validation with time series of surface elevation to guarantee correct interpretation of the signal.

More information on highly accurate surface elevation change measurements in space and time using photogrammetry and position sensors can be found here: https://doi.org/10.1002/eco.2114 .

PS: in (more) natural peatlands seasonal elevation change may reach well beyond 5 cm, and swelling induced by individual rain events can be detected as well as day-night fluctuations related to evapotranspiration and groundwater recharge. Highly dynamic!

Hello,

I have done several peat thickness measurements for my PhD and research using manual proving... it is time consuming but perhaps better that any RS techniques for the moment. It is not the definitive method but very easy to check.

Peat subsidence I have read some good paper about InSAR but you also could do some fix markers that are attached to the mineral soil?

All the best!