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

## **Abstract** \n\nThis dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied:\n\n\n\nMrVBF 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.\n\n\n\nThe 3 second resolution product was generated from the 1 second MrVBF product and masked by the 3" water and ocean mask datasets.\n\n## **Dataset History** \n\nData quality \n\nLineage: \n\n\n\nSource data\n\n1.\tThe 1 second MrVBF product\n\n2.\t3 second resolution SRTM water body and ocean mask datasets\n\n\n\nMrVBF calculation\n\nThe 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.\n\n\n\nEach 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.\n\n\n\nValue Threshold Resolution Interpretation\n\n slope (%) (approx)\n\n 0 30 m Erosional\n\n 1 16 30 Small hillside deposit\n\n 2 8 30 Narrow valley floor\n\n 3 4 90\n\n 4 2 270 Valley floor\n\n 5 1 800 Extensive valley floor\n\n 6 0.5 2.4 km\n\n 7 0.25 7.2 km Depositional basin\n\n 8 0.125 22 km\n\n 9 0.0625 66 km Extensive depositional basin\n\n\n\nThe 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.\n\n\n\nMrVBF has been used with topographic wetness index (TWI) to predict soil depths; see McKenzie, Gallant and Gregory (2003) for details.\n\n\n\n\n\nPositional accuracy: \n\nThe 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.\n\n\n\nAttribute accuracy: \n\nMrVBF 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:\n\n\\*\tIn 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.\n\n\\*\tAlluvial and colluvial fans are depositional but stand above their surroundings so often appear as erosional features with MrVBF = 0.\n\nThe 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.\n\n\n\nLogical consistency:\n\nThis product is a consistent representation of terrain based on the information in DEM-S.\n\n\n\nCompleteness:\n\nThe 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.\n\n## **Dataset Citation** \n\nCSIRO (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.

**摘要**

本数据集及其元数据声明由第三方提交至生物区域评估计划（Bioregional Assessment Programme），此处按原始提交内容完整呈现：

多分辨率谷底平坦度指数（Multi-resolution Valley Bottom Flatness, MrVBF）是一款地形指数，旨在基于两项观测特征识别不同尺度下的沉积物质分布区域：谷底相较于周边区域地势低平，且大型谷底较小型谷底更为平坦。指数值为0时对应侵蚀地形，值为1及以上则代表沉积区域面积愈发广阔。现有研究证据表明，MrVBF数值与沉积物质深度存在相关性。

本3秒分辨率产品由1秒分辨率MrVBF产品生成，并通过3秒分辨率水体与海洋掩膜数据集完成掩膜处理。

**数据集历史**

### 数据质量

#### 数据溯源

1. 1秒分辨率MrVBF产品
2. 3秒分辨率航天飞机雷达地形测绘任务（Shuttle Radar Topography Mission, SRTM）水体与海洋掩膜数据集

#### MrVBF计算方法

MrVBF的计算方法详见Gallant与Dowling（2003）的研究成果。该方法基于由原始数字高程模型（Digital Elevation Model, DEM）及逐步泛化的DEM计算得到的坡度与景观位置（3单元格或6单元格圆形窗口内的排名）。用于生成本次产品的算法版本为6g-a5，与原始论文中的算法存在细微差异。

每个MrVBF值均与特定尺度及坡度阈值绑定。每递增一个数值，坡度阈值减半，计算尺度则扩大为原来的三倍。在每个尺度下，若某位置地势较高（在周边单元格中排名位居多数以上）或坡度大于设定阈值，则被判定为侵蚀区域，反之则为沉积区域。每个点位取其最大的对应指数值作为最终判定结果，因此指数值为0代表该点位在所有尺度下均被判定为侵蚀区域。

| 指数值 | 坡度阈值（%） | 近似分辨率 | 含义解释 |
| :----: | :----------: | :--------: | :------: |
| 0 | —— | 30 m | 侵蚀地形 |
| 1 | 16 | 30 m | 小型山坡沉积区 |
| 2 | 8 | 30 m | 狭窄谷底 |
| 3 | 4 | 90 m | —— |
| 4 | 2 | 270 m | 谷底 |
| 5 | 1 | 800 m | 广阔谷底 |
| 6 | 0.5 | 2.4 km | —— |
| 7 | 0.25 | 7.2 km | 沉积盆地 |
| 8 | 0.125 | 22 km | —— |
| 9 | 0.0625 | 66 km | 大型沉积盆地 |

3秒分辨率的MrVBF产品通过对每3×3组1秒分辨率单元格取中位值，由1秒分辨率MrVBF产品推导得到。

MrVBF已与地形湿度指数（Topographic Wetness Index, TWI）结合，用于预测土壤深度，详细信息可参见McKenzie、Gallant与Gregory（2003）的研究。

#### 位置精度

水平位置误差与原始SRTM 1秒数据一致，在澳大利亚境内90%的检测点位误差不超过7.2米。更多相关信息详见Rodriguez等人（2006）的研究。

#### 属性精度

MrVBF旨在表征以坡积和冲积过程为主的景观内的沉积程度，该指数在澳大利亚大部分地区的多种应用场景中均被证明具有实用价值。但在以下情形中可能产生误导：
* 在以风蚀搬运为主的区域，该方法的假设前提不成立，沙丘等地形会被判定为侵蚀特征（MrVBF值为0）。
* 冲积扇与坡积扇属于沉积区域，但地势高于周边区域，因此常被判定为侵蚀特征（MrVBF值为0）。
由于生成DEM-S所使用的SRTM数据特性，平坦景观中常存在小型凸起区域，此类区域大概率为数据伪影，MrVBF在这些特征上通常会显示较小值或0。

#### 逻辑一致性

本产品是基于DEM-S中的信息对地形的一致性表征。

#### 完整性

MrVBF产品的覆盖范围与源数据DEM-S一致，几乎涵盖澳大利亚大陆及近岸岛屿。部分包含大陆或岛屿部分区域的瓦片未提供1秒分辨率数据，因此存在缺失，详细信息请参见DEM-S元数据。

**数据集引用**

澳大利亚联邦科学与工业研究组织（CSIRO，2000）：3秒分辨率多分辨率谷底平坦度指数（MrVBF），CSIRO 20000211。生物区域评估源数据集。2018年12月12日查阅，http://data.bioregionalassessments.gov.au/dataset/7dfc93bb-62f3-40a1-8d39-0c0f27a83cb3.