Merrick LiDAR Mapping Data Collection

Image: Color relief map of the triangulated irregular network (TIN) of the classified LiDAR bare-earth points for the entire area of Leon County. Red depicts the higher topography at approximately 200 feet above sea level. Blue depicts the lowest points at or around sea level.The maps are under the purview of TLC GIS, an interlocal partnership of the City of Tallahassee, the Leon County Board of County Commissioners, and the Leon County Property Appraiserâs Office, that was established in 1990 to create a joint geographic information system (GIS) for use by a variety of local public agencies. From 2005 - 2008, to effectively and consistently accomplish the mapping update, TLC GISâ strategy had been to divide the county into three urban and six rural sections and fly one urban and one rural section each year for data collection (under a contract awarded to Merrick in 2005). Thus, all urban areas were updated every three years and all rural areas every six years. With the change in Florida legislation in June, 2008, the funding processes were adjusted and those changes impacted TLCâs strategies and scheduling for land base map updating. The Florida Department of Revenue (DOR) had traditionally been responsible for having all Florida counties flown and, with the change in legislation, counties larger than 25,000 population would have to reimburse the DOR or opt out of having their county flown by the state agency. TLC GIS took advantage of opting out, but became required to fly the entire county in one single flight every three years, thus prompting the need for a new approach and schedule for acquiring updated data on a regular basis.Initial Data Collection ProgramMerrick has been providing services to TLC GIS since 2001 in the form of program management, aerial photography, aerotriangulation, softcopy photogrammetric updating of digital terrain models (DTMs), planimetry, contour generation, and aerial image orthorectification services. What started as a routine project for the agency and the consultant in early 2001, quickly changed following the initial delivery of the first collected data. Now, the approach is changing again to accommodate TLC GISâ new data acquisition plan and schedule. The first modification in data acquisition arose when the interlocal agency adopted a change-detection based update strategy (to leverage as much of the investment in the existing landbase as possible, in contrast to the previous strategy of compiling the land base anew every five years). Accompanying that issue were the differing opinions about the accuracy of the existing photogrammetrically compiled topographic data among the interlocal user community. Thus, in 2002, Merrick worked closely with TLC GIS to evaluate the systems and procedures and identify the optimum solution for providing the agency with the data required to address the mapping needs of all the agencies involved. LiDAR was selected as the best technology to use. TLC GIS was one of the first public agencies in Florida to use LiDAR in the acquisition of mapping data. Since those initial days in 2001/2002, Merrick has provided updates of different portions of the county, per the agencyâs planned acquisition strategy. Now, under the agencyâs adjusted program and the existing contract, Merrick will provide data collection for the entire county. The orthoimagery will meet or exceed the Florida Department of Revenueâs requirements.New Strategy in TLC GISâ Data Collection ProgramTLCGIS began this new approach to data acquisition with the completion of their initial single flight in January, 2009. For that first flight, Merrick provided ortho imagery and LiDAR mapping to accomplish the data collection on a single pass. Approximately 750 square miles were mapped using the remote sensing technology, with the collected data providing information on topography, vegetation, structures, water ways, and current drainage patterns. The collected mapping data will be used in support of a variety of programs for the city and county, for example public works, police, fire, community development, utilities, sheriffâs office, emergency management, elections, technology, telecommunications, cooperative extensive, county appraiserâs, and planning departments as well as by the county school board.Advantages of LiDAR For a Single-Flight ProgramOne of the major advantages of using LiDAR in their single-flight map updating is the accuracy and completeness of data.Lee Hartsfield, TLCGIS Coordinator explained, âLiDAR provides us with the ease of obtaining accurate land data that is of a much higher quality than what has been produced in the past with traditional technology. Beyond that, the Landbase information we receive from Merrick is the foundation for all our GIS data. TLC GIS maintains over 380 GIS data layers of information which are tied to this base information. The accuracy and completeness in the base layer is everything.âGreg Mauldin, GIS Scientist and Project Manager adds, âLeon County is heavily forested and itâs difficult to obtain complete topographic data from the standard stereo imagery. Starting in 2009, Merrickâs LiDAR is providing us with a DTM that is more accurate than anything to date. They are collecting the LiDAR data at an accuracy specification that will support the generation of one-foot contours, in accordance with our specifications. We need that level of accuracy for flood risk analysis in numerous low-lying, relatively flat areas within Leon County.âMauldin goes on to say, âWeâve learned weâre also economically benefiting from the use of LiDAR because it offsets some of the field work that is normally needed for engineering projects. The existing LiDAR data is accurate enough to minimize the need to deploy surveying teams for the planning phase of capital improvement projects. We already have much of the topographic information we need through the LiDAR collection, thus weâve eliminated a significant portion of pre-project surveying and saved some dollars. Moreover, the increased accuracy of the new 2009 data is sufficient to support engineering design phase of many projects.âCost Benefits of LiDAR ProgramAs a leader in the use of LiDAR, TLC GIS understands the benefits of the technology. Itâs faster, easier, more accurate, more cost effective, more complete, and leads to higher quality derivative mapping from the base information. With the program, TLC GIS has been able to meet their budgets, while enhancing the overall quality, accuracy, and timing of the data.âIn todayâs economy, every public dollar spent is being evaluated and the prudent use of those public dollars is a top priority for us,â says Hartsfield. âUsing LiDAR for data acquisition provides the opportunity to be financially responsible, while providing us with highly accurate data that serves multiple agenciesâ multiple needs. It allows us to optimize every dollar we spend.âAn increasing number of public agencies are taking advantage of the benefits of using LiDAR for their mapping needs. From flood plain mapping and emergency preparedness to environmental habitat modeling, water management, and public infrastructure planning, LiDAR is growing in use and popularity.Merrick, a $75 million geospatial mapping, engineering, architecture, design-build, and surveying firm, serves domestic and international clients in the government, energy, life sciences, infrastructure, and mapping markets. With a focus on the highly technical field of geospatial surveying and remote sensing, the firmâs most recent work includes providing mapping services for the U.S. Army Corps of Engineers; Cook County, IL; Xcel Energy; and the U.S. Air Force Space Command.

Author: Merrick & Company press release

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