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)

Estimation of Sounding Uncertainty from Measurements of Water Mass Variability

Analysis techniques are introduced that allow for estimation of potential sounding uncertainty due to water mass variability from reconnaissance campaigns in which oceanographic parameters are measured at a high temporal and spatial resolution. The analysis techniques do not require sounding data, thus analyses can be tailored to match any survey system; this allows for pre-analysis campaigns to optimize survey instrumentation and sound speed profiling rates such that a desired survey specification can be maintained. Additionally, the output of the analysis methods can potentially provide a higher fidelity estimation of sounding uncertainty due to water mass variability than uncertainty models in common use

Uncertainty Wedge Analysis: Quantifying the Impact of Sparse Sound Speed Profiling Regimes on Sounding Uncertainty

Recent advances in real-time monitoring of uncertainty due to refraction have demonstrated the power of estimating and visualizing uncertainty over the entire potential sounding space. This representation format, referred to as an uncertainty wedge, can be used to help solve difficult survey planning problems regarding the spatio-temporal variability of the watercolumn. Though initially developed to work in-line with underway watercolumn sampling hardware (e.g. moving vessel profilers), uncertainty wedge analysis techniques are extensible to investigate problems associated with low-density watercolumn sampling in which only a few sound speed casts are gathered per day. As uncertainty wedge analysis techniques require no sounding data, the overhead of post-processing soundings is circumvented in the situation when one needs to quickly ascertain the impact of a particular sampling regime. In keeping with the spirit of the underlying real-time monitoring tools, a just in time analysis of sound speed casts can help the field operator assess the effects of watercolumn variability during acquisition and objectively seek a watercolumn sampling regime which would balance the opposing goals of maximizing survey efficiency and maintaining reasonable sounding accuracy. In this work, we investigate the particular problem of estimating the uncertainty that would be associated with a particular low-density sound speed sampling regime. A pre-analysis technique is proposed in which a high-density set of sound speed profiles provides a baseline against which various low-density sampling regimes can be tested, the end goal being to ascertain the penalty in sounding confidence that would be associated with a particular low-density sampling regime. In other words, by knowing too much about the watercolumn, one can objectively quantify the impact of not knowing enough. In addition to the goal-seeking field application outlined earlier, this allows for more confi- dent attribution of uncertainty to soundings, a marked improvement over current approaches to refraction uncertainty estimation

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

A procedure for developing an acceptance test for airborne bathymetric lidar data application to NOAA charts in shallow waters

National Oceanic and Atmospheric Administration (NOAA) hydrographic data is typically acquired using sonar systems, with a small percent acquired via airborne lidar bathymetry for near‐shore areas. This study investigated an integrated approach for meeting NOAA’s hydrographic survey requirements for near‐shore areas of NOAA charts, using the existing topographic‐bathymetric lidar data from USACE’s National Coastal Mapping Program (NCMP). 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’s bathymetric lidar data are evaluated through a comparison to NOAA’s Office of Coast Survey hydrographic data derived from acoustic surveys. As a result, it is possible to assess if NCMP’s bathymetry can be used to fill in the data gap shoreward of the navigable area limit line (0 to 4 meters) and if there is potential for applying NCMP’s bathymetry lidar data to near‐shore areas deeper than 10 meters. Based on the study results, recommendations will be provided to NOAA for the site conditions where this data will provide the most benefit. Additionally, this analysis may allow the development of future operating procedures and workflows using other topographic‐ bathymetric lidar datasets to help update near‐shore areas of the NOAA charts

ICESat-2 Bathymetry:Advances in Methods and Science

Since the 2018 launch of NASA's ICESat-2 mission, one capability of its Advanced Topographic Laser Altimeter System (ATLAS) that has far exceeded expectations is bathymetric measurement. Although ICESat-2 was designed to generate surface-specific along-track and gridded data products, bathymetry was not a pre-launch science requirement of the mission. However, since launch, ATLAS has proven capable of bathymetric measurement to &gt;40m in very clear waters [1], and ICESat-2 bathymetry is being used in a growing number of science disciplines. Post-launch efforts have focused on bathymetric signal classification (sea surface, water column and seafloor) and correction for refraction at the air-water interface. Because ATLAS provides bathymetry only along discrete tracks, another area of focus is on integration of ATLAS data with relative bathymetry from multispectral satellite imagery-often referred to as satellite-derived bathymetry (SDB)-to obtain spatially-contiguous 2D bathymetric coverage. This paper synthesizes the latest algorithms, techniques and uses of ICESat-2 bathymetry, including collaborative efforts of the Bathymetry Working Group of the ICESat-2 Science Team, and recommends topics for future investigation.</p