Based on the processing of CZMIL data collected in Hawaii during a JALBTCX mission (2013) and in the Pacific for The Ocean Cleanup project (October, 2016), we demonstrate the possibility of reliably estimating the seawater column’s optical properties from lidar waveforms in deep clear (Jerlov class I and IB) waters. With minor improvements to the data processing method previously applied to Florida survey data (2003, 2006, 2012–2017), we estimate the diffuse attenuation coefficient at the wavelength of 532 nm, Kd (532), to be 0.045–0.060 m-1 in both regions. The results are in good agreement with space satellite data for the days of the lidar surveys and with Jerlov’s Kd curves for water classes I and IB.
CZMIL is an integrated lidar-imagery system and software suite designed for highly automated generation of physical and environmental information products for coastal zone mapping in the framework of the US Army Corps of Engineers (USACE) National Coastal Mapping Program (NCMP). This paper presents the results of CZMIL system validation in turbid water conditions along the Gulf Coast of Mississippi and in relatively clear water conditions in Florida in late spring 2012. Results of the USACE May-October 2012 mission in Green Bay, WI and Lake Erie are presented. The system performance tests show that CZMIL successfully achieved 7-8m depth in Mississippi with Kd =0.46m-1 (Kd is the diffuse attenuation coefficient) and up to 41m in Florida when Kd=0.11m-1. Bathymetric accuracy of CZMIL was measured by comparing CZMIL depths with multi-beam sonar data from Cat Island, MS and from off the coast of Fort. Lauderdale, FL. Validation demonstrated that CZMIL meets USACE specifications (two standard deviation, 2σ, ~30 cm). To measure topographic accuracy we made direct comparisons of CZMIL elevations to GPS-surveyed ground control points and vehicle-based lidar scans of topographic surfaces. Results confirmed that CZMIL meets the USACE topographic requirements (2σ, ~15 cm). Upon completion of the Green Bay and Lake Erie mission there were 89 flights with 2231 flightlines. The general hours of aircraft engine time (which doesn't include all transit/ferry flights) was 441 hours with 173 hours of time on survey flightlines. The 4.8 billion (!) laser shots and 38.6 billion digitized waveforms covered over 1025 miles of shoreline.
The U.S. Army Corps of Engineers (USACE) began developing airborne lidar bathymetry systems for coastal mapping
applications in 1986, and fielded its first system in 1994. In the ensuing years, the Scanning Hydrographic Operational
Airborne Lidar Survey research and development program led to the creation of the Joint Airborne Lidar Bathymetry
Technical Center of Expertise (JALBTCX), a robust federal government partnership in airborne lidar bathymetry; the
USACE National Coastal Mapping Program, a program of mapping built around airborne lidar bathymetry and
complementary airborne remote sensing technologies; and a healthy commercial field of airborne lidar bathymeter
manufacturers and service providers. The Coastal Zone Mapping and Imaging Lidar (CZMIL) is a new USACE sensor
development effort and a partnership among the JALBTCX, Optech International, and The University of Southern
Mississippi. The goal of CZMIL is to produce an integrated lidar and imagery sensor suite and software package
designed for highly automated generation of physical and environmental information products for the coastal zone.
CZMIL is an opportunity to revamp existing hardware and software to address the turbidity and shallow water
limitations of existing systems; improve environmental applications of the data; take advantage of advances in laser,
scanner, and receiver technology, and in signal processing and data fusion algorithms; while maintaining accurate depth
measurement capability. The CZMIL program has been underway since 2006, resulting in a detailed design of the
CZMIL software and hardware. CZMIL fabrication will be complete in 2010 and fielded in USACE operations in 2011.
CZMIL is a new airborne mapping and imaging system designed to simultaneously produce high resolution 3D images
of the beach and shallow water seafloor, and to achieve benthic classification and water column characterization. It is
designed to have high performance in shallow, turbid waters. The Data Acquisition System (DAS) is composed of a new
bathymetric lidar integrated with a commercial imaging spectrometer and digital metric camera. The Data Processing
System (DPS) employs new algorithms and software designed to automatically produce environmental image products
by combining data from the three sensors within a data fusion paradigm. CZMIL is specifically designed to meet the
requirements of the USACE Coastal Mapping Program, and is scheduled to enter field trials in the spring of 2011.
Passive, hyperspectral image data and bathymetric lidar data are complimentary data types that can be used effectively in tandem. Hyperspectral data contain information related to water quality, depth, and bottom type; and bathymetric lidar data contain precise information about the depth of the water and qualitative information about water quality and bottom reflectance. The two systems together provide constraints on each other. For example, lidar-derived depths can be used to constrain spectral radiative transfer models for hyperspectral data, which allows for the estimation of bottom reflectance for each pixel. Similarly, depths can be used to calibrate models, which permit the estimation of depths from the hyperspectral data cube on the raster defined by the spectral imagery. We demonstrate these capabilities by fusing hyperspectral data from the LASH and AVIRIS spectrometers with depth data from the SHOALS bathymetric laser to achieve bottom classification and increase the density of depth measurements in Kaneohe Bay, Hawaii. These capabilities are envisioned as operating modes of the next-generation SHOALS system, CHARTS, which will deploy a bathymetric laser and spectrometer on the same platform.
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