Consideration of Level of Confidence within Multi-Approach Satellite-Derived Bathymetry

René Chénier,Mesha Sagram,Ryan Ahola,Yask Shelat,Marc-André Faucher

doi:10.3390/ijgi8010048

Abstract

The Canadian Hydrographic Service (CHS) publishes nautical charts covering all Canadian waters. Through projects with the Canadian Space Agency, CHS has been investigating remote sensing techniques to support hydrographic applications. One challenge CHS has encountered relates to quantifying its confidence in remote sensing products. This is particularly challenging with Satellite-Derived Bathymetry (SDB) where minimal in situ data may be present for validation. This paper proposes a level of confidence approach where a minimum number of SDB techniques are required to agree within a defined level to allow SDB estimates to be retained. The approach was applied to a Canadian Arctic site, incorporating four techniques: empirical, classification and photogrammetric (automatic and manual). Based on International Hydrographic Organization (IHO) guidelines, each individual approach provided results meeting the CATegory of Zones Of Confidence (CATZOC) level C requirement. By applying the level of confidence approach, where technique combinations agreed within 1 m (e.g., all agree, three agree, two agree) large portions of the extracted bathymetry could now meet the CATZOC A2/B requirement. Areas where at least three approaches agreed have an accuracy of 1.2 m and represent 81% of the total surface. The proposed technique not only increases overall accuracy but also removes some of the uncertainty associated with SDB, particularly for locations where in situ validation data is not available. This approach could provide an option for hydrographic offices to increase their confidence in SDB, potentially allowing for increased SDB use within hydrographic products.

Highlights

The Canadian Hydrographic Service (CHS) is responsible for providing hydrographic products and services to ensure safe, sustainable and navigable use of Canada’s waterways
In terms of the total surface of bathymetry extracted after application of the four Satellite-Derived Bathymetry (SDB) methods, the manual photogrammetric extraction was the approach that provided the most SDB coverage, followed by classification, empirical and the automatic photogrammetric extraction approaches (Figure 4)
The manual photogrammetric technique extracted 100% of the area for depths from 0–20 m, which was followed by 81% from classification, 59% from the empirical method and 39% from the automatic photogrammetric approach

Summary

Introduction

The Canadian Hydrographic Service (CHS) is responsible for providing hydrographic products and services to ensure safe, sustainable and navigable use of Canada’s waterways. CHS investigations of empirical [9] and photogrammetric [10] SDB techniques have illustrated the potential of these approaches for deriving accurate bathymetry estimates in Canadian waters. While representing excellent progress for estimating water depth from satellite imagery, significant challenges remain with providing hydrographic offices (HOs) with sufficient confidence in SDB estimates to allow the information to be incorporated into official nautical products. As CHS demonstrated in [9] and [10], SDB obtained through various techniques can regularly achieve CATZOC level C. While this represents a reasonable accuracy for satellite-derived information, there is a desire by HOs to improve their confidence in SDB results. CATZOC determinations can only be obtained when in situ bathymetric information is available, limiting HO confidence in SDB results when only limited or no in situ depth information is available

Methods

Results

Conclusion