Satellite-Derived Bathymetry a Reconnaissance Tool for Hydrography

In some developing countries, the information available to plan and prioritise hydrographic surveys is typically based on visual inspection of existing nautical charts. However, due to the age of many existing charts and lack of availability of the original source data from which they were compiled (e.g., smooth sheets) this type of analysis is often quite limited. A study was conducted to evaluate the use of a satellite-derived bathymetry (SDB) procedure to map shallow-water bathymetry in a GIS environment, and to identify areas that require a new hydrographic survey. Publically available, multispectral satellite imagery and published algorithms are used to derive estimates of the bathymetry. The study results indicate a potential use of the procedure by national hydrographic offices as a reconnaissance too

ALB Evaluation for NOAA charting requirements

The National Oceanic and Atmospheric Administration (NOAA) acquires hydrographic data around the coasts of the US and its territories using in-house surveys and contracting resources. Hydrographic data are primarily collected using sonar systems, while a small percent is acquired via Airborne Lidar Bathymetry (ALB) for nearshore areas. NOAA has an ongoing requirement, as per the Coast and Geodetic Survey Act of 1947, to survey nearshore areas as part of its coastal mapping activities, including updating nautical charts, creating hydrodynamic models and supporting coastal planning and habitat mapping. NOAA has initiated a project to investigate the potential use of ALB data from non-hydrographic survey programmes (i.e., programmes designed to support objectives other than nautical charting and with specifications and requirements that differ from those of NOAA hydrographic surveys) in order to increase the amount of data available to meet these nearshore mapping requirements. THIS PAPER PRESENTS AN evaluation of ALB data from the US Army Corps of Engineers (USACE) National Coastal Mapping Program (NCMP) for use by NOAA’s Offi ce of Coast Survey (OCS). Th ese NCMP datasets were evaluated through a statistical comparison to bathymetric surfaces derived from hydrographic NOAA surveys. Th e objectives of the analysis were: 1. to assess the level of agreement between the NCMP and OCS data in areas of overlap in a variety of coastal environments and 2. to determine whether NCMP ALB survey data can be compiled with NOAA OCS hydrographic data to generate seamless shallowbathymetry digital elevation modes (DEMs)

Develping a Methodology for the Mapping and Characterization of the Nigerian Coastline Using Remote Sensing

Coastline delineation is important in maritime boundary determination, as well as for analyzing coastline change rates due to coastal erosion, sea level change, storms, and other causes. Coastline change rate estimates depend on the uncertainty of the current and historical coastlines used in the analysis, which, in turn, depend on the surveying technologies and techniques that were originally used. Current techniques for coastline mapping include photogrammetric delineation using tide-coordinated aerial imagery. However, in many developing countries, the charted coastlines may have been inadequately and inconsistently mapped largely due to inadequate resources. This paper describes the use of an automated technique for coastline mapping and classification that is based on satellite imagery. A spectral analysis using different image bands can be used to define the land/water boundary and characterize the coastal area around the coastline. A first-order uncertainty analysis was also performed. The satellite-derived coastlines were compared to charted coastlines to evaluate the adequacy and consistency of the charted coastlines. The satellite-derived coastlines were also compared to coastlines derived from historical maps to assess changes and change rates. The results of the coastline uncertainty analysis were then used to compute propagated uncertainties in coastline change rate estimates and to gain greater insight into actual changes. The procedure was developed in a GIS environment using study sites along the Nigerian coastline. However, this procedure can be applied to other poorly charted/mapped coastal areas as well

Beyond the Chart: The use of Satellite Remote Sensing for Assessing the Adequacy and Completeness Information

Chart adequacy and completeness information consists of the symbols, abbreviations and warnings used to inform mariners of the level of confidence that should be given to data on a nautical chart. This information is derived both from the nautical chart and sailing directions. However, analysis based solely on these datasets is limited without access to the sources (e.g., smooth sheets). Publically-available, multi-spectral satellite imagery and published algorithms can be used to derive estimates of the relative bathymetry in shallow, clear waters. In this study, we evaluate the potential of these methods for supplementing the procedure to assess the adequacy of hydrographic surveying and nautical charting coverage. Optically-derived bathymetry provides information in areas that have not been surveyed and monitor any seafloor changes that may have occurred since the last survey of the area. Preliminary results show that multi-spectral satellite remote sensing is also potentially beneficial as a reconnaissance tool prior to a hydrographic acoustic survey

Spectral characterization of the Nigerian shoreline using Landsat imagery

The challenges of shoreline mapping include the high costs of acquiring up-to-date survey data over the coastal area. As a result, in many developing countries, the shoreline has not been consistently mapped. The variety of methods used for this mapping and the large time differences between the surveys (on the order of decades) could result in inaccuracies in shoreline data. This study presents the development of a shoreline characterization procedure for the Nigerian coastline using satellite remote sensing technology. The study goal is to produce a complete, consistent and continuous shoreline map using publicly available data processed in a GIS environment. A spectral analysis using different satellite bands was conducted to define the land/water boundary and characterize the coastal area around the shoreline. The satellite-derived shorelines were compared to charted shorelines for adequacy and consistency. The procedure was developed based on study sites along the Nigerian coastline. Although the shoreline characterization procedure is developed based on datasets from Nigeria, the procedure should be suitable for use in mapping other developing areas around world

Development of a Geo-spatial Analysis Methodology for Assessing the Adequacy of Hydrographic Surveying and Nautical Charts

IHO Publication C-55 (Status of Hydrographic Surveying and Nautical Charting Worldwide) contains information about the progress of hydrographic surveying and nautical charting for a country with navigable waters under its jurisdiction. Listed primarily as percent coverage, it is difficult to use this information to determine: 1) if the current level of surveying or charting is adequate or in need of action, or 2) can be used to compare different locations. An analysis and assessment methodology has been developed to assess the adequacy hydrographic surveying and nautical charting coverage. Indications of chart adequacy and completeness as depicted on current charts or sailing directions are spatially correlated with significant maritime sites/areas associated with social, environmental and economic factors. The procedure was developed in a GIS environment for Belize and Nigeria. Areas within the charts were prioritized based on zone of confidence, source diagrams, chart quality symbols/indicators, doubtful danger markings, survey completeness, navigationally-significant depths, and areas of significant maritime importance

New Approaches for Evaluating Lidar-Derived Shoreline

This study presents and compares two new methods of assessing the uncertainty of lidar-derived National Shoreline mapped by NOAA’s National Geodetic Survey: an empirical (ground-based) approach and a stochastic (Monte Carlo) approach. OCIS codes: (280.3640) Lidar; (120.2830) Height measurements; (000.4430) Numerical approximation and analysi

Future directions in hydrography using satellite-derived bathymetry

Satellite remote sensing provides useful reconnaissance tool for mapping near-shore bathymetry, characterizing a coastal area and monitoring any seafloor changes that may have occurred since the last hydrographic survey of the area. At the 2012 Canada Hydro conference, a study was presented on the potential use of Landsat satellite imagery to map shallow-water bathymetry in a GIS environment over three study sites. Since then, several collaborations between the current study group and various hydrographic organizations were established with the goal of implementing optically-derived bathymetry as part of their data acquiring procedure. Bathymetry over additional study sites around the world was tested. Also, different commercial software packages were evaluated to provide an affordable processing platform for hydrographic offices in developing countries. In this paper, an overview will be provided on the advances that have been achieved in the past year and an update and future directions of the study

Monitoring Near-Shore Bathymetry Using a Multi-Image Satellite-Derived Bathymetry Approach

ABSTRACT Two advanced survey systems for hydrographic surveying are multi-beam echsounder (MBES) and airborne lidar bathymetry (ALB). Compared to more traditional hydrographic surveying methods, these systems provide both highly accurate and a dense coverage of depth measurements. However, high cost and logistic challenges that are required for either type of hydrographic survey operation limit the number of surveys and coverage area that can be conducted. As a result, most survey efforts primarily focus on updating existing chart information, and do not provide more enhanced charting capabilities, such as identifying dynamic seafloor areas or monitoring changes due to natural disasters (e.g., hurricanes, floods, or tsunamis) along the charted coastlines. An alternative reconnaissance approach is the use of Satellite Derived Bathymetry (SDB). Although SDB provide bathymetry products at a coarser spatial resolution compared to MBES or ALB, satellite imagery can be repeatedly collected over the same area. In addition, some of the multi-spectral satellite imagery is publically-available, and at low at no cost. In this paper, we describe a practical approach that is based on a multitemporal analysis of the SDB using Landsat 8 imagery. The study results presented here are based on a time series of two sites (Barnegat Bay Inlet, NJ and Nantucket Sound, MA). Preliminary results indicate that it is possible to identify both stable and dynamic seafloor areas that have implications for charting and coastal zone management application

Developing an acceptance test for non-hydrographic airborne bathymetric lidar data application to NOAA charts in shallow waters

Hydrographic data of the National Oceanic and Atmospheric Administration are typically acquired using sonar systems, with a small percent acquired via airborne lidar bathymetry for nearshore areas. This study investigates an integrated approach to meeting NOAA’s hydrographic survey requirements for nearshore areas of NOAA charts using existing U.S. Army Corps of Engineers (USACE) National Coastal Mapping Program (NCMP) topographic-bathymetric lidar (TBL) data. Because these existing NCMP bathymetric lidar datasets were not collected to NOAA hydrographic surveying standards, it is unclear if, and under what circumstances, they might aid in meeting certain hydrographic surveying requirements. The NCMP bathymetric lidar data were evaluated through a comparison against NOAA’s hydrographic Services Division (HSD) data derived from acoustic surveys. Key goals included assessing whether NCMP bathymetry can be used to fill in the data gap shoreward of the navigable area limit line (0 to 4 m depth) and if there is potential for applying NCMP TBL data to nearshore areas deeper than 10 m. The study results were used to make recommendations for future use of the data in NOAA. Additionally, this work may allow the development of future operating procedures and workflows using other topographicbathymetric lidar datasets to help update nearshore areas of the NOAA charts