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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Jul 2018

Research article | 06 Jul 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Earth Surface Dynamics (ESurf).

Measuring Decadal Vertical Land-level Changes from SRTM-C (2000) and TanDEM-X (~ 2015) in the South-Central Andes

Benjamin Purinton and Bodo Bookhagen Benjamin Purinton and Bodo Bookhagen
  • Institute of Earth and Environmental Science, Universität Potsdam, Potsdam, Germany

Abstract. Vertical change is often measured in the cryosphere via digital elevation model (DEM) differencing to assess glacier and ice-sheet mass balances. This requires the signal of change to outweigh the noise associated with the datasets. On the ice-free earth, land-level change is much smaller in magnitude and thus requires more accurate DEMs for differencing and identification of change. Previously, this has required high-resolution data at small scales. For the first time we measure land-level changes at the scale of entire mountain belts in the south-central Andes using the SRTM-C (collected in 2000) and the TanDEM-X (collected from 2010–2015), both spaceborne radar DEMs. Long-standing errors in the SRTM-C are corrected using the TanDEM-X as a control surface and applying cosine-fit co-registration to remove ~1/10 pixel (~3m) shifts, Fast Fourier Transform and filtering to remove SRTM-C short- and long-wavelength stripes, and blocked shifting to remove remaining complex biases. The datasets are then differenced and outlier pixels are identified as potential signal for the case of gravel-bed channels and hillslopes. We are able to identify signals of incision and aggradation (with magnitudes down to ~3m in best case) in two >100km river reaches, with increased geomorphic activity downstream of knickpoints. Anthropogenic gravel excavation and piling is prominently measured, with magnitudes exceeding ±5m (up to >10m for large piles). These values correspond to conservative rates of 0.2 to >0.5m/yr for vertical changes in gravel-bed rivers. For hillslopes, since we require stricter cutoffs for noise, we are only able to identify one major landslide with a deposit volume of 16±0.15×106m3. Additional signals of change can be garnered from TanDEM-X auxiliary layers, however, these are more difficult to quantify. The methods presented can be extended to any region of the world with SRTM-C and TanDEM-X coverage where vertical land-level changes are of interest, with the caveat that remaining vertical uncertainties in primarily the SRTM-C limit detection in steep and complex topography.

Benjamin Purinton and Bodo Bookhagen
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Benjamin Purinton and Bodo Bookhagen
Model code and software

Correction and Differencing Scripts (Python) B. Purinton

Benjamin Purinton and Bodo Bookhagen
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Publications Copernicus
Short summary
We show a new and novel use for the SRTM-C digital elevation model from February 2000 and the newer TanDEM-X dataset from ~ 2015. We difference the datasets over hillslopes and gravel-bed channels to extract vertical land-level changes. These signals are associated with incision, aggradation, and landsliding. This requires careful correction of the SRTM-C biases using the TanDEM-X, with the possibility to extend the method to moderate relief areas with SRTM-C and TanDEM-X coverage.
We show a new and novel use for the SRTM-C digital elevation model from February 2000 and the...