Multi-resolution Valley Bottom Flatness MrVBF at three second resolution CSIRO 20000211

Abstract

This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied:

MrVBF is a topographic index designed to identify areas of deposited material at a range of scales based on the observations that valley bottoms are low and flat relative to their surroundings and that large valley bottoms are flatter than smaller ones. Zero values indicate erosional terrain with values 1 and larger indicating progressively larger areas of deposition. There is some evidence that MrVBF values correlate with depth of deposited material.

The 3 second resolution product was generated from the 1 second MrVBF product and masked by the 3" water and ocean mask datasets.

Dataset History

Data quality

Lineage:

Source data

1. The 1 second MrVBF product

2. 3 second resolution SRTM water body and ocean mask datasets

MrVBF calculation

The MrVBF method is described in Gallant and Dowling (2003). It is based on slope and position in landscape (ranking within a 3- or 6-cell circular window) calculated from the original DEM and progressively generalised DEMs. The algorithm used to create this product is version 6g-a5, which is slightly different to that in the original paper.

Each value of MrVBF is associated with a particular scale and slope threshold. For each successive value the slope threshold halves and the scale triples. At each scale a location is considered erosional if it is high (ranked above the majority of the surrounding cells) or steep (slope greater than the threshold), and depositional otherwise. The largest value takes precedence at each location, so a value of zero indicates the site is considered to be erosional at all scales.

Value Threshold Resolution Interpretation

     slope (%)    (approx)

0 30 m Erosional

1 16 30 Small hillside deposit

2 8 30 Narrow valley floor

3 4 90

4 2 270 Valley floor

5 1 800 Extensive valley floor

6 0.5 2.4 km

7 0.25 7.2 km Depositional basin

8 0.125 22 km

9 0.0625 66 km Extensive depositional basin

The 3 second version of MrVBF was derived from the 1 second MrVBF using the median value in each 3 x 3 group of 1 second cells.

MrVBF has been used with topographic wetness index (TWI) to predict soil depths; see McKenzie, Gallant and Gregory (2003) for details.

Positional accuracy:

The horizontal positional error is the same as for the raw SRTM 1 second data, with 90% of tested locations within 7.2 m for Australia. See Rodriguez et al. (2006) for more information.

Attribute accuracy:

MrVBF is designed to represent the degree of deposition within a landscape dominated by colluvial and alluvial processes and the index has been found helpful for various purposes in much of Australia. There are several circumstances where it can be misleading:

* In areas dominated by aeolian transport the assumptions behind the method are not met, and dunes (for example) are represented as erosional features with MrVBF = 0.

* Alluvial and colluvial fans are depositional but stand above their surroundings so often appear as erosional features with MrVBF = 0.

The characteristics of the SRTM data from which DEM-S has been derived means that there are often small raised areas within otherwise flat landscapes that may be artefacts; MrVBF will often have a small value or 0 on those features.

Logical consistency:

This product is a consistent representation of terrain based on the information in DEM-S.

Completeness:

The MrVBF product covers the same area as the source DEM-S, which is virtually all of continental Australia and near coastal islands. Some tiles containing parts of mainland or pieces of islands were not supplied at 1 second resolution and are therefore missing, see DEM-S metadata for details.

Dataset Citation

CSIRO (2000) Multi-resolution Valley Bottom Flatness MrVBF at three second resolution CSIRO 20000211. Bioregional Assessment Source Dataset. Viewed 12 December 2018, http://data.bioregionalassessments.gov.au/dataset/7dfc93bb-62f3-40a1-8d39-0c0f27a83cb3.