Feature: Lamp & Lidar
Aerial Mapping Fall '13 - Aerial Mapping Fall '13
A 77-year-old aerial mapping firm successfully employs new technologies on major infrastructure improvement projects.
By Aixa G. Lopez, PE
Aerial surveying and mapping professionals offer a wide range of technologies that provide public agencies with new ways to expedite the renovation and construction of infrastructure projects. One important reason for employing these advanced technologies is their ability to develop accurate, three-dimensional models safely, with only limited, if any, disruption to heavy vehicular traffic.
Robinson Aerial Surveys, Inc. (Robinson) has been commissioned for years by agencies in New Jersey and New York to provide aerial mapping services using technologies such as color, digital, low-altitude aerial mapping photography (LAMP) and laser imaging detection and ranging (lidar). Established in 1936, Robinson was founded by a civil engineer who worked for the New York State Park Commission and was contracted by the U.S. Department of Agriculture to photograph 16,000 square miles in New York State. Today, Robinson has its own photographic laboratory, digital and analytical mapping systems, and CADD platforms.
LAMP is a helicopter-based camera system. It uses a Wild RC-30 aerial mapping camera with forward motion compensation (FMC) and is stabilized in the three axes using a gyroscopic mount. The combination of the slower forward speed of the helicopter and the use of FMC allows for unparalleled clarity in the photographic image. The improved image clarity allows for ground control points to be observed much more closely than with conventionally flown photography. This in turn allows the control network to be held to a much greater accuracy.
This latest in digital sensors provides imagery clarity even in low-light environments such as during the winter months or in the deep shadow of city streets. Because these digital sensors collect wavelengths of light across a wide portion of the spectrum, they have the added ability to acquire black and white, color, and color infrared imagery all within the same photo mission.
Using LAMP is the safest technical approach to creating a new Digital Terrain Model (DTM) of hard, paved surfaces and the right-of-way corridor. It keeps surveyors out of harm’s way while using their expertise to collect required ground data for a fully integrated DTM.
LAMP is useful for a wide range of surveying projects, including street planning, power line organizing and patrolling, pipeline preparing and patrolling, park organizing, subdivision arranging, and railroad preparing and patrolling. It is either manually or automatically performed from a helicopter, typically, and surveying organizations that carry out LAMP make the helicopter arrangements.
Lidar and photogrammetric mapping complement each other in that where photogrammetry is better suited for a quick, qualitative analysis in determining the identity of surface features, lidar data allows for large areas of three-dimensional data to be collected in a cost-effective manner.
PATH Rail System
Over the past five years, Robinson has been contracted to produce topographic mapping for three separate projects along the PATH rail system by the Port Authority of New York. First, the company produced 1”=40’ topographic mapping with one‐foot contours and established ground control for the entire length of the system that was open to the sky and visible from aerial photography. Second, it was contracted to develop highly accurate topographic mapping for the Harrison Station Modernization Project using LAMP, producing 1”=30’ topographic mapping with contours at .2 ft. intervals. Most recently, it has been contracted to again fly LAMP imagery for the portion of the PATH corridor from Station 458+00 to 288+00 on the east bound (NY bound) and 458+00 to 360+00 on the west bound rails under the “PATH Leasing” project.
All topographic mapping was provided in Auto-CAD format in New Jersey State Plane Coordinate System, NAD83, and NAVD88 in accordance with Port Authority Standards set forth in the “Data Collection and Drafting” manual. All visible features were mapped in addition to significant break lines, approximate centerlines of swales and/or ditches, tops and bottom of banks to the project limits in open areas. All features were located to an accuracy of no less than 0.10’ vertically and horizontally, and digital ortho- photographs were provided at a scale of 1 “=40’.
The New Jersey Department of Transportation (NJDOT) proposed to replace the I87 Bridge over Absecon Inlet between Atlantic City and Brigantine, New Jersey. The proposed bridge replacement project was undertaken in order to improve the sole means of access to the Brigantine community.
LAMP services and photogrammetric base mapping at a scale of 1”=30’ with one-foot contour interval were provided. Photogrammetric mapping from LAMP was used in order to reduce the overall cost of the base mapping effort. The improved image clarity allowed for ground control points to be observed much more closely than with conventionally flown photography. This permitted the control network to be held to a much greater accuracy. The technology provides highly accurate 3D data for the roadway surface on overpasses and bridge superstructures.
The use of LAMP also allowed areas that were prone to dense traffic to be accurately mapped with minimal impact on traffic flow and more safely by reducing field personnel’s exposure to hazardous situations. The staff used LAMP at a nominal scale of 1”= 100’. The photography was taken at an altitude of 600 feet above the mean terrain, letting the survey grade accuracies be achieved through photogrammetric mapping.
Use of these technologies in infrastructure work has proven to be convenient, efficient, and cost-effective. Some of the general advantages include:
- Large amount of detail that can be interpreted visually.
- Faster data collection and map data that can be produced much more quickly that using traditional techniques.
- Printed aerial photos that are useful in fieldwork to provide the “bigger picture.” Field staff can see the terrain that is visible from their viewpoint in the wider context of the surrounding area.
- Facilitation of logistics such as traffic management, field coordination, etc.
John F. Kennedy International Airport
Robinson helped the Port Authority of New York and New Jersey (PANYNJ) develop an obstruction chart for John F. Kennedy International Airport (JFK) and submit data to the FAA Airport GIS portal and the PANYNJ Interactive Airport Layout Plan system. In addition, Robinson proposed to obtain and use low-altitude lidar data for the initial portion of the runway obstruction survey as well as the ortho-image generation.
Because lidar data sets are obtained by using an “active sensor” and do not depend on solar angle, they can be flown at night, avoiding the heaviest air traffic periods around JFK & LaGuardia airports. In addition to being safer by not over-congesting the already crowded airspace, these flights were also advantageous in getting “leaf-on” digital elevation model (DEM) data quickly prior to the fall foliage drop in early November.
Robinson also proposed to use a Microsoft UltraCam X digital sensor for this project rather than a conventional aerial camera. This provided such benefits as better quality imagery to base the project on and both airborne GPS (ABGPS) and inertial measuring unit (IMU) technology to strengthen the control network and ease the aero-triangulation process. The better image quality came from the sensor’s ability to collect up to 12-bit RGB imagery, allowing for more wavelengths of visible light to be used in photogrammetric compilation. The digital sensor negated any foreign object obscuration (e.g. dust, hair, scratches, etc.) to enter the ortho-rectification process, thus improving the look and accuracy of the final product.
After imagery flight, Robinson selected the required photo-identifiable photogrammetric ground control points, authorizing the surveyors (KS Engineers) to begin establishing the supplemental GPS ground control. The established points were semi-permanent, and tie sheets with sketches were provided in accordance with the FAA’s AC 150/5300-16A “General Guidance and Specifications for Aeronautical Surveys: Establishment of Geodetic Control and Submission to the National Geodetic Survey.”
Robinson proceeded with the “relative” and “interior” orientations using the ABGPS/IMU data and digitally tied each image together, creating a preliminary photo mosaic or “block.” Robinson editors used the lidar DEM and triangulated aerial images to create the ortho-rectified digital photos.
We then used the lidar data set to perform the initial classification of obstructions protruding through the approach plane as provided to the Port Authority. Robinson inspected for any transmission antennae that was not “visible” to the lidar and inspected each protruding object or structure for its highest point. These points were field-verified by the surveyors using conventional survey methods and confirmed using photogrammetric processes.
The use of lidar data also helped with scheduling. Our team was able to begin to identify potential obstructions, allowing the survey crews to start their field checks even prior to completing the imagery flight.
Large transportation infrastructure projects such as these present three major obstacles to data collection: scale (the sheer size of the projects), accessibility to the subject properties (it’s hampered by traffic concerns), and safety (putting survey crews in harm’s way is unacceptable). Fortunately, firms tasked with collecting data under these challenging environments have at their disposal advanced technology such as LAMP and aerial lidar to make data collection, fast, accurate, and safe.
Aixa G. Lopez, P.E
. is the marketing and business development manager for Robinson.
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