TCarta | Satellite Derived Bathymetry

TCarta Marine

Bathymetric survey techniques have greatly evolved over the last 200 years.

What is satellite derived bathymetry (SDB)?

SDB relates the surface reflectance of shallow coastal waters to the depth of the water column. This process has been greatly refined and developed in recent years:

  • In 1975, bathymetry in the Bahamas and off the coast of Florida was calculated to a depth of 22 meters by NASA and Jacques Cousteau using Landsat 1.
  • The US Navy used the GEOSAT satellite to create the first global bathymetric dataset of the deep ocean in the mid 1980's.
  • Since early 2000's, physics-based radiative transfer models have become a popular means of determining the bathymetry of coastal regions using very high resolution satellite imagery.

Although SDB will never rival multibeam and lidar in terms of accuracy, precision and resolution, it can be used as a reconnaissance tool for planned bathymetric surveys as well as to fill gaps in existing survey data coverage. In certain situations, SDB is a more viable option than traditional methods for surveying coastal environments.

How is SDB produced?

Imagery Collection

A remote sensing analyst will first decide the type of imagery product that best suites the area of interest, considering factors like spatial, temporal, spectral, and radiometric resolutions. Next, candidate imagery will be visually investigated for desirable qualities such as having minimal cloud cover, haze, turbidity/waves, and sun glint. Imagery used is always within the past 5 years unless historic imagery is desired by the customer.

Pre-Processing

In most instances, the imagery we collect already comes radiometrically and geometrically corrected from the provider. Digital number values from the satellite sensor are converted to top of atmosphere radiance values then further to water surface reflectance. In this process, atmospheric correction is undergone to adjust for scattering and absorption effects, while de-glinting is done on a per need basis. Land, clouds, whitecaps, and vessels are masked out by thresholding the NIR band.

Bathymetry Creation

A physics-based radiative transfer algorithm, which incorporates satellite observed surface reflectance and properties of the water column, is used to produce our bathymetry products.

Post-Processing

A smoothing filter is applied as needed to remove signal noise, and the bathymetry output is evaluated in a 3D environment to remove all erroneous data points. Additionally, any artificial objects, which cause inaccurate depth readings, are cleaned up. Examples of such include algae blooms, raised sediment, dredging channels, waves/turbidity, boats/docks, underwater cables, building/cloud shadows, and dark vegetation.

Quality Assurance / Quality Control

Our final step is to compare our SDB product against any and all in situ data for the study area and assign an uncertainty level (10, 20 or 30%) to the SDB output. SDB is then delivered to the customer.

How do we know it works?

Remotely Validating SDB

It is very difficult to validate SDB in some regions due to a lack of available ground truth data. However, as a participant in the Applied User’s program for NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2), TCarta Marine has developed methods to extract highly accurate space-based laser bathymetry (SBL) from ICESat-2's data products.

SBL data have shown to have as high as 95% accuracy when compared to in situ airborne LiDAR surveys. These data provide a worldwide dataset that is currently being used at TCarta to validate SDB depth retrievals. These technological developments provide a path forward to standardizing SDB survey practices for inclusion in wider hydrographic applications. 

How can SDB be used?

TCarta has produced SDB for clients around the world with a wide range of end-use applications.

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Climate Change Resiliency

Tarawa, Republic of Kiribati

The Republic of Kiribati is one of the most vulnerable nations in the world to the effects of sea level rise from changing climate. TCarta Marine produced satellite derived bathymetry and seafloor classification maps to aid in management and mitigation decisions.

Disaster Response and Recovery

Antigua and Barbuda

As hurricanes become more numerous and increasingly intense, it is important to understand how they effect the bathymetry of affected nations for both ecological and humanitarian purposes. TCarta Marine produced SDB for the islands of Antigua and Barbuda before and after Hurricane Irma to help managers understand these changes.

Coastal Modeling

Yanaha Island, Japan

The coastal environment is an ever evolving and fluid system. In order to model these changes, TCarta produced a seamless topobathy surface to aid in a coastal siting project in Japan.

Arctic Mapping

Gjoa Haven, Nunavut, Canada

Due to rising temperatures, more and more of the Arctic thaws each year. Most of these areas have only been surveyed for navigational channels even though more than 50% of the world's shallow waters are located in the Arctic with most of it uncharted. TCarta has produced SDB in a variety of areas in the Arctic.

Coastal Engineering

Sound of Iona, Scotland

SDB provided modern bathymetry for a pipeline siting project to assist engineers in finding the best location to route pipelines between Isle of Iona and the mainland in eastern Scotland.

Want to know more?

For more information on Satellite Derived Bathymetry, start a conversation with TCarta today.

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