Tetra Tech’s Geomatics Technologies Group provides accurate mapping and data measurement via remotely sensed technologies. Our ASPRS-certified photogrammetrists, remote sensing professionals and GIS analysts bring more than a century of collective industry experience utilizing state-of-the-art mapping software, airborne sensors and camera systems and a robust IT infrastructure. Our experience together includes extensive work on projects requiring data collection and analysis, GIS, photogrammetric mapping, orthoimagery, LiDAR, multi and hyperspectral technology, and airborne magnetrometry. Our team is supported by a vast network of Tetra Tech professionals specializing in a wide range of GIS applications, data management & visualization, programming, software development and all aspects of environmental consulting. With a full suite of services, the Geomatics Technologies Group is committed to providing unique solutions and high quality products to meet each client’s project needs.
Areas of Expertise
Airborne LiDAR (Light Detection and Ranging) technology uses laser pulses to measure distances in order to create accurate, high resolution, digital elevation data. Airborne LiDAR data applications include contour mapping, corridor mapping, vegetation mapping, transmission line mapping, shoreline mapping, and slope analysis. Tetra Tech has been providing LiDAR services and solutions using an array of LiDAR processing software, including the industry standard TerraSuite, and ArcGIS based LP360.
High Resolution Orthoimagery
Orthoimagery combines the visual attributes of high resolution aerial imagery with the geometry, spatial accuracy and reliability of a planimetric map. Orthoimagery has become the standard backdrop and base-data for many GIS. Orthoimagery ground resolutions vary with typical resolutions at 1’, ½’ or ¼’ ground sample distance. The imagery can be delivered as RGB color, color infrared, or multispectral.
Photogrammetry precisely measures three-dimensional coordinates of points on an aerial photo using overlapping (stereo) images and sophisticated algorithms to solve for the unknown locations of the spatial content. Tetra Tech has extensive experience producing engineering-scale (1”=20’, 1”=40’) maps of planimetric features and topographic contours. End-product deliverables are customized to client standards and file formats, including Microstation (.dgn), AutoCAD (.dwg), ArcGIS GRID and PLS-CADD. Tetra Tech uses the latest stereo collection platform - the Cardinal System’s VrTwo softcopy.
Hyperspectral and Multispectral Technology
Hyperspectral and multispectral sensors capture many wavelength bands with the electromagnetic spectrum. The imagery can be used to map vegetation cover and other land characteristics and is particularly effective in the detection of vegetation species, vegetation stress, leaf area index, and soil characteristics which are used to understand ecosystem functions, vegetation growth, and nutrient cycling as well as predict biophysical characteristics.
Geographic Information Systems (GIS)
Tetra Tech’s GIS capabilities include data development and analysis, data conversion and editing, and cartographic production. Much of our work utilizes ArcGIS software for information management and decision support for environmental management. Our GIS analysts have expert knowledge of our full in-house ESRI software line. Our GIS work is supplemented by the proficient use of Microsoft Office suites, MapInfo Professional, Adobe Acrobat Professional and Creative Suite.
Image classification is either spectral or object based in nature. As a rule, the approach chosen to classify a particular image is based highly on the characteristics of the image and on what classes must be discerned from the data. Spectral classification is generally a good approach for lower resolution images such as Landsat (30m pixels). OBIA is generally appropriate for higher resolution imagery such as NAIP (1m pixels).
Aerial magnetics is a geophysical remote sensing technique that can be used to locate subsurface metallic objects. The Earth's magnetic field interacts with metallic objects resulting in a secondary magnetic field. The secondary magnetic field is identified and modeled to determine its source and defining characteristics. Processing considers many factors including remanent magnetization, magnetic susceptibility, source depth, and source geometry. Tetra Tech uses aerial magnetics to locate subsurface pipelines, utilities, unexploded ordnance, archaeological sites, faults and other geologic phenomena.
Aerotriangulation (AT) is the basis for geometric accuracy and a critical component of each project. Aerotriangulation really commences with careful project planning and design; properly designed ground control, and flight layout and cross strips are crucial for a successful AT solution. Tetra Tech uses Inpho’s Match-AT, widely recognized as the prime aerotriangulation tool, for both manual and automated AT.
3D Digital Terrain Models
DTMs are 3D representations of bare-earth surfaces and provide topographic information. The Geomatics Technologies Group creates and analyzes DTMs for environmental, engineering, mining, and infrastructure applications. Digital contour maps are derived from DTMs to supply land surveyors elevation data without the need for complete field surveys. Tetra Tech has the capabilities to derive DTMs from LiDAR or aerial imagery to support an array of client needs.
Airborne thermal sensing provides temperature analysis information for a wide variety of applications including flow measurement of streams and rivers, loss of heat in pipelines, power lines and substations, animal counts/tracking, and determination of moisture on rooftops. Thermography is also used to study algae blooms, landfills, coal mines, geothermal systems and bridges. Our remote sensing professionals can manage the project beginning with acquisition, to analysis, to delivery in a geo-referenced format.