National Aeronautics and Space Administration

Wallops Flight Facility

EAARL

THE EXPERIMENTAL ADVANCED AIRBORNE RESEARCH LIDAR

The EAARL (Experimental Advanced Airborne Research Lidar) is a new airborne lidar that provides unprecedented capabilities to survey coral reefs, nearshore benthic habitats, coastal vegetation, and sandy beaches. The EAARL sensor suite includes a raster-scanning-water penetrating full-waveform adaptive lidar, a down-looking color digital camera, an array of precision kinematic GPS receivers which provide for sub-meter geo-referencing of each laser and hyper spectral sample. It will soon also include a hyperspectral scanner.

EAARL has the unique real-time capability to detect, capture, and automatically adapt to each laser return backscatter over a large signal dynamic range and keyed to considerable variations in vertical complexity of the surface target. These features enable automatic adaptive acquisition of dramatically different surface types in a single EAARL overflight. This makes EAARL uniquely well suited for mapping applications such as coral reefs, bright sandy beaches, coastal vegetation, and trees where extreme variations in the laser backscatter complexity and signal strength are caused by different physical and optical characteristics.

The EAARL system builds on knowledge and experience gained through the development and refinement of the Airborne Oceanographic Lidar (AOL), the Airborne Topographic Mapper (ATM), and the Scanning Radar Altimeter (SRA). A “full waveform digitizing” concept was first used on the AOL in 1996 (Wright, 2001), and again in 1998 on the SRA (Wright, 1999). The EAARL system described here combines shallow bathymetric and topographic mapping capabilities and features in a single system which can be deployed to undertake coastal cross-environment surveys of shallow submerged topography, sub-aerial topography, and vegetation covered topography in a single flight.

Present Activities:

Activity 1—Coral Reef Maps

Coral reefs and their associated communities of seagrasses, mangroves and mudflats are extremely sensitive indicators of water quality and the ecological integrity of the ecosystem. They tolerate narrow ranges of temperature, salinity, water clarity, and other chemical and water quality characteristics. Reefs thus are excellent sentinels of the quality of their environment. They are also important fishery and nursery areas, and more recently have proved to be very important to regional economies as tourist attractions. Reefs provide protection from storms and erosion to coastlines and provide sand for beaches. Proper monitoring of reefs can identify changes in water quality or impacts from land-based activities. Monitoring changes in water quality and coral reef geomorphology can help local resource managers understand the implications of actions occurring in watersheds that are associated with particular coral communities. These connections will help in development of sound management plans for coral reefs and other coastal and marine resources.

Synoptic maps of coral communities based on satellite images generally portray only coarse geomorphological zones and are not sufficiently detailed or accurate to be of high value to biologists. Aircraft-based hyperspectral sensors can acquire finer scale images, but are generally quite expensive. Further, water-column contamination of the light reflected from reef benthic classes diminishes the accuracy of thematic maps derived from passive aircraft or spacecraft. The EAARL is intended to mitigate these difficulties by combining a hyperspectral scanner with a laser bathymetric sounder on a light twin piston engine aircraft.

We are collaborating with Dr. John Brock of the USGS in developing detailed, high density, precision lidar submerged topographic baseline maps of selected coral reefs in the Florida Keys. We are collaboratively developing advanced software analytical tools specifically targeted at creating low cost, fine scale, regional, coral reef base maps and wide area fine scale coral reef benthic change detection methods based on lidar data. Our goal is to provide a sensitive low cost tool which will permit coral reef managers to make accurate informed decisions with regard to coral reef health. We are working in cooperation with NOAA and National Park Service coral reef managers.

Activity 2—Seagrass and Coastal Habitat Applications

We are also collaborating with Dr. Tonya Clayton of the USGS and Dr. Chuanmin Hu of the University of South Florida in developing new sea grass applications of the EAARL system to extend remote sensing methods beyond boundary delineation of spatial extent to include the remote estimation of seagrass standing crop and the use of seagrass-habitat parameters as a sort of keystone indicator of the health of coastal systems. We are also interested in investigating the possibility of using the additional information contained in the returned laser pulse (waveform) for the purposes of coastal benthic habitat mapping and classification.

Activity 3—Riverine Environments

Extensive maps of riverine geomorphological features plus biological data is critical for understanding habitat and predicting population distribution of birds and aquatic species, e.g., endangered mussels, fish. Field collection is frequently prohibitive. The concurrent forest and water penetrating adaptive laser backscatter capability of EAARL is being investigated and developed as a low cost method of rapidly obtaining critical data for riverine habitat managers. A mission was conducted to acquire experimental data over such a riverine environment in August, 2001 over the Cacapon River in western Virginia.

The morphology of alluvial river channels is determined by relatively complicated mutual interaction between the pattern of flow in the channel, the transport of sediment through the channel as suspended load and bedload, and the topography of the bed and banks of the channel. The local flow field is determined by the shape of the channel, the sediment transport is determined primarily by the flow and sediment particle characteristics, and the pattern of erosion and deposition produced by the sediment-transport field determines the morphology of the channel bed and banks. Thus, the flow, sediment transport, and the channel morphology are inextricably linked and, as a result, developing a mechanistic understanding of river channel behavior requires that the interactions among these three fields be adequately characterized in the precise terms of mathematics and physics. This project specifically addresses fluid and sediment-transport physics within the context of river channel morphodynamics. The goal of the project is to carry out field investigations using the EAARL instrument and to develop an accurate topographic map of the exposed and submerged portions of the the river bed.

Activity 4—Coastal Bays

A coastal bay supports one of the world’s most productive natural systems. Estuaries are where salt water from the ocean and fresh water mix. They are nurseries for young shrimp, crabs, and fish. More than 70% of all fish, shellfish, and crustaceans spend some critical stage of their development in coastal bay waters where they are protected from larger predators that live the open ocean.

The shoreline and adjacent shallow areas of many coastal bays is very shallow, and very dynamic. It is also frequently very difficult to access or survey using traditional marine or terrestrial methods. The EAARL system offers several unique capabilities with respect to monitoring the shallow regions (0-3m) of coastal bays through remote sensing. Since the system illuminates a relatively small area (20cm diameter) on the surface, very little temporal pulse spreading occurs as the pulse is reflected and refracted at the water’s surface. We are collaborating with NOAA and the USGS in a Tampa Bay project.

Educational Outreach

Two of the graduate students selected for the first Goddard Coastal Zone Research Fellowship are working with the EAARL instrument and data this summer. Both students are being exposed to the latest lidar technology as beginning graduate students instead of waiting until they get their first postgraduate position. Each student has already made important contributions to the project and each is being challenged to examine several different aspects of the EAARL project and identify a potential thesis topic.

We have also reached out to local universities to identify high achieving students who may be interested in gaining some practical experience in remote sensing and experience working on a NASA research project. As a result of this effort, we have hired a third under graduate summer student from Salisbury University’s Math and Computer Science department.

Future/Planned Directions:

Activity 1—Compound Sensor

Add passive hyperspectral sensor and develop methods that will create an enhanced combined effect between the EAARL lidar and the hyperspectral sensor. Once the accuracy of the EAARL bathymetric lidar has been verified, the EAARL hyperspectral scanner will be added. At that point, the benthic cover classification phase of the EAARL project will be initiated. Of particular interest will be an assessment of the capability to remotely map morphology and cover type within the study area. As unknown water depth fundamentally limits remote-mapping accuracy (Holden and LeDrew, 1998; Mumby et al., 1998). The EAARL compound sensor is expected to afford significant improvement.

Activity 2—Surface, Littoral, and Mixed Layer Wave Measurement

We are interested in using the EAARL system to study surface waves and wave effects in the littoral zone, suspended sediment transport, and also enhancing the EAARL system with a nadir pointing high power water penetrating laser to investigate the potential of lidar for measuring the mix layer. The EAARL system is uniquely suited for mixed layer investigation because it already contains a wide dynamic range laser receiver which can be used to detect and digitize deep vertical laser profiles while simultaneously capturing the surface wave field with it’s scanning laser.

Educational Outreach

We plan to participate in the GCR in 2003 and to expand our outreach efforts with local universities.

Collaborators:

Lead Investigator: C. Wayne Wright