Paul E. LaRocque

Design considerations for achieving high accuracy with the SHOALS bathymetric lidar system

The ultimate accuracy of depths from an airborne laser hydrography system depends both on careful hardware design aimed at producing the best possible accuracy and precision of recorded data, along with insensitivity to environmental effects, and on post-flight data processing software which corrects for a number of unavoidable biases and provides for flexible operator interaction to handle special cases. The generic procedure for obtaining a depth from an airborne lidar pulse involves measurement of the time between the surface return and the bottom return. In practice, because both of these return times are biased due to a number of environmental and hardware effects, it is necessary to apply various correctors in order to obtain depth estimates which are sufficiently accurate to meet International Hydrographic Office standards. Potential false targets, also of both environmental and hardware origin, must be discriminated, and wave heights must be removed. It is important to have a depth confidence value matched to accuracy and to have warnings about or automatic deletion of pulses with questionable characteristics. Techniques, procedures, and algorithms developed for the SHOALS systems are detailed here.

New Capabilities of the “SHOALS” Airborne Lidar Bathymeter

Abstract The technology and methodology of airborne laser bathymetry are far from mature, and new capabilities continue to be attained. The SHOALS lidar system was recently augmented with the ability to utilize kinematic GPS (KGPS) with on-the-fly (OTF) phase ambiguity resolution to permit the system to be used more extensively over land and for shoreline and other topographic mapping, in addition to underwater bathymetry. The seamless integration of these capabilities permits continuous surveying across the land/water boundary. Importantly, this also permits the production of sea bottom and topographic elevations without the need for concurrently measured water-level data. Algorithms and procedures associated with the use of OTF KGPS are presented along with examples of performance.

Design description and field testing of the SHOALS-1000T airborne bathymeter

The SHOALS-1000T is the first generation of coastal mapping systems which incorporates both airborne lidar bathymetric (ALB) and airborne topographic subsystems. Its predecessor, the SHOALS (Scanning Hydrographic Operational Airborne Lidar Survey) system went operational in 1994 and was retired in 2003 after a history of successful worldwide surveys. The SHOALS-1000T has 2.5 times the data collection rate of the previous SHOALS system and yet is about one-third the size and consumes about half the power. A description of the system design will be given, along with a summary of extensive field testing carried out in Florida in August of 2003. It will be shown that despite the reduction in size and power requirements, the basic system performance matched the previous system very well. The increased collection rate also increases other capabilities such as target detection. The addition of a digital camera has enhanced the SHOALS-1000T system as a premier coastline mapping tool.

Galaxy: a new state of the art airborne lidar system

Recent advancements in lidar technologies have led to significant improvements in Teledyne Optech’s airborne lidar systems. This paper will present the performance enhancements that have led to the creation of the Galaxy, a compact scanning lidar system. Unlike the previous generation of conventional airborne lidar, the Galaxy offers fundamentally improved specifications for long-range airborne lidar systems. The Galaxy system is capable of acquiring high-density, multiple-return data with unique pulse separation characteristics and exceptional precision. Utilizing discrete time-of-flight measurement electronics, this new system is capable of seamlessly operating at very high laser repetition rates through blind zones and with multiple pulses in the air. By utilizing even higher scan products , the system outperforms previous generations of systems and optimizes point density during collection.

Rapid 2-axis scanning lidar prototype

The rapid 2-axis scanning lidar prototype was developed to demonstrate high-precision single-pixel linear-mode lidar performance. The lidar system is a combined integration of components from various commercial products allowing for future customization and performance enhancements. The intent of the prototype scanner is to demonstrate current stateof- the-art high-speed linear scanning technologies. The system consists of two pieces: the sensor head and control unit. The senor head can be installed up to 4 m from the control box and houses the lidar scanning components and a small RGB camera. The control unit houses the power supplies and ranging electronics necessary for operating the electronics housed inside the sensor head. This paper will discuss the benefits of a 2-axis scanning linear-mode lidar system, such as range performance and a userselectable FOV. Other features include real-time processing of 3D image frames consisting of up to 200,000 points per frame.

The History of Laser Bathymetry

This paper gives a coarse-grained historical overview of activities in airborne Lidar hydrography (ALH), starting with the general operating principles of the technique, then followed by a synopsis of the principal, worldwide ALH efforts over the past two and a half decades. This will lead to a discussion of the design trade-offs and performance of the SHOALS system, Optech Inc’s recently concluded ALH program for the US Army Corps of Engineers. Finally, a comparison is given of the current ALH operational capabilities (depth, area coverage, accuracy, reliability, cost-effectiveness) to the currently used acoustic methods.