Presentation on theme: "Lidar Data Applications for Natural Resource Management"— Presentation transcript:
1Lidar Data Applications for Natural Resource Management Tom Bobbe, Mark Finco, Ken Brewer, Denise LaesUSDA Forest ServiceRemote Sensing Applications CenterSalt Lake City, UtahGeospatial 2007 ConferenceThursday - May 10, 2007
2Presentation Outline Lidar system fundamentals Resource management applicationsDigital Terrain ModelsVegetation ModelsLidar applications in the Forest ServiceLidar acquisition specifications
3Fundamentals of Lidar Lidar Basics: Lidar = Light Detection And RangingScanning Infrared Laser Rangefinderthousand pulses per second result in typical point densities between 8 per 1-m2 to 1 per 4-m2 (called post spacing)Multiple returns from a single pulse are possibleCoupled with IMU/GPS provides very accurate X,Y,Z point clouds (~15-cm in Z).In the most general sense, the fundamental principals of lidar are very simple … and as the 1st speaker they should be presented very briefly …Lidar is an acronym …Lidar provides measurements from which images can be derived … not images themselvesAt a lidar system’s heart is a laser rangefinder and a survey grade gps… add a scanning system and lidar systems can acquire 100,000 or more height measurements every secondMost modern systems can collect multiple (often 4) height measurements from each pulse of the laser – point out example in figure of 2 returnsThese height measurements are actually distance from laser measurements … coupled with GPS/IMU they create what we call DIGITAL TERRAIN MODELS (to differentiate them from digital elevation models)
4Characteristics of Lidar Data Point data, but …Large volume of dataAssume: 1 to 4 pulses / m2Assume: 2 returns per pulseAssume: 6 values per returnEquals: 0.38 – GB per acre, or – TB per 10,000 acresBecause of data volumeOften standard GIS analyses don’t workRequire special pre-processing for analysisPoint data, but this is complicated by the volume of data that needs to be analyzedLarge volume of dataAssume: 1 to 4 pulses / m2Assume: 2 returns per pulseAssume: 6 attributes per return … e.g., x, y, z, I, angle, return #Equals: 0.38 – GB per acre, or – TB per 10,000 acresBecause of data volume …Often standard GIS analyses don’t work … or work so slowly that they aren’t practicalMany times tempted to move away from the vector format and quickly turn into a raster, but this amounts to throwing information awayRequire special pre-processing for analysis. This includes tiling the data into smaller, more manageable, chunksHow big is your study area?Consider these characteristics before diving in …The image is of a study area in western Montana (Lubrecht Expt’l Forest) – 77k acres, 2km tiles for analyzability
5Examples of Lidar Point Clouds This lidar point cloud transect crosses a forest roadPoints Colored by HeightHighestLowestThese are simply examples of what lidar point clouds look like colored by elevation.The top image – lidar can be used as a profiler to investigate road cuts and gradients. Note that individual trees are visible within the point cloud.The bottom image – Lidar data, however, is collected using either a fixed wing aircraft or helicopter. The resulting dataset can be viewed as a 3-d point cloud. Note in this forested image that there are some man-made structures which are visible under the canopy.In this 3-D perspective of a lidar point cloud note the buildings
6Multiple return lidarAll Returns3rd Return4th Return2nd Return1st ReturnMultiple return lidar contributes to forest structure measurements1st return is not just top of canopyLast (4th) return is not just the groundFirst analytical step typically filters ground returns from all returnsFigures Courtesy of PNW Seattle Laboratory
7Primary Application – High Resolution DTM The first application for lidar data was the creation of high resolution Digital Terrain ModelsNote: we use the acronym DTM not DEM because DEM is a data format and is usually assumed to be a USGS product. DTM is a more generic term.The largest federal user is FEMA for flood plain mappingThis slide visually demonstrates how the 3-d point cloud can be used to generate high resolution Digital Terrain Models (DTM).The lidar points above the ground are typically discarded … vegetative overburdenThe magic of lidar data analysis is the separation of ground returns from above ground returnsClick and the point cloud transitions to a shaded relief mapNote: it becomes obvious that this area is a road intersection. The main road also has a 2-track path or frontage road merging with it.
810-m DEM / 1-m Lidar DTM Comparison USGS 10-meter Digital Elevation Model (DEM)Lidar-derived 1-m Digital Terrain Model (DTM)Site ASite ASite BSite BThis is a comparison of a 10-m USGS DEM and the 1-m Lidar-derived DTMDifferences are obvious. Micro-topography in the lower left hand side of the image is interesting.Two sites – A and B – are going to be compared at larger scale in the next slide.These high resolution DTMs seem to answer a lot of questions … but they also raise a few moreFor example, if you have a 1-m DTM and there is a 36” stump on the ground … should it be included in the DTM as part of the “terrain”? (do we have a choice?)New and important features are recognizable on the 1-meter digital terrain model (micro-hydrologic patterns, roads / trails, and other man-made features)
9Comparison Areas USGS 10-meter Digital Elevation Model (DEM) Lidar-derived 1-m Digital Terrain Model (DTM)Site AThe comparison of site A shows that an earthen dam is easily discernable in the 1-m lidar DTM, but wholly un-recognizable in the 10-m DEM. Also note the road system leading to and away from the dam.The site B comparison simply shows the micro relief in the 1-m DTMThough interesting visual comparisons, these sites and other comparisons have practical implications for engineering applications. Consider, for example the improved cut-and-fill estimates and run-off/erosion calculations that could be created with 1-m DTMs.Site B
10DTM’s are just the beginning however … Tools are being developed in the Forest Service and commercial sector to extract information about the vegetationIndividual Tree Measurements (potentially height, crown base height, crown diameter depending on crown spacing)Canopy Height, Cover, DensityVegetation Structural CharacteristicsIn addition to the bare earth DTM’s, the lidar data contains a wealth of information about the vertical distribution of vegetation (structure) on the landscape.While these applications are relatively new (<5 years for areas of any size) they are rapidly being facilitated by new software being developed within the Forest Service and commerciallySome of the leaders in resource application development are right here in the USFSPNW Seattle Lab – McGaughy and Reutebuch … application called FUSION for lidar data visualization and analysisFUSION is distributed and supported by RSAC … (say more?)RMRS researchers in Moscow, Idaho (and Others) are developing resource analysis methods and other applications …
11Fusion SoftwareDeveloped by USDA Forest Service Pacific Northwest (PNW) Research Station (McCaughey, Reutebuch & Andersen)Originally intended for PNW internal useRSAC agreed to distribute and provide support for FS usersCapabilities include:View lidar data quickly and easilyHandles almost any format of lidar dataCreates surfaces (bare earth models (DTMs), canopy surface models)QA/QC of vendor-processed dataEasily measures heights of featuresLarge number of forestry-related measurementsAnd much more…* One lidar analysis tool, FUSION, which was developed at USFS PNW in Seattle allows for (among many other things) the measurement of individual trees.
14Vegetation information starts with DTMs Raw lidar returns (Colored by height)DTMAll returns normalized by the DTMDTM extraction is a necessary 1st step in most vegetation analyses …The image shows the progression from raw lidar points (top), to bare earth DTM (middle), to lidar points that are normalized based on the DTM … this changes the color scheme and you can see tall trees in the front and right of the image that were not visualizeable without the normalization.
15USFS PNW’s FUSION Software Individual Tree MeasurementsFUSION facilitates many types of measurements …One set of tools are provided to individual trees …Other tools allow for the summarization of the lidar returns over larger areas
16Lidar and ground measurements relationships Strong relationships with ground measured variablesHeight, Basal Area, Volume, Crown Bulk Density, etc.Relationships verified by numerous researchersMcGaughy, Reutebuch & Andersen (USFS PNW)Hudak and Evans (USFS RMRS)Lefsky (Colorado State)Evans (Mississippi State)Wynne (Virginia Tech)Popescu (Texas A&M)Naesset (Norway)Many others …Dominant height (r 2 = 0.98)Relationships between lidar data and ground-based forestry measurements are very strong …Modeled height, BA, Volume, CBD and other structural variables are strongestSome work (primarily at PNW) has been done to use the intensity attribute provide additional information (e.g., sub-lifeform)These relationships have been confirmed by many researchers... The next challenge is to use these relationships to meet an operational mapping objectiveFigures Courtesy of PNW Seattle Laboratory
17Lidar Applications in the USFS Recent tally of lidar applications in the USFS (Lachowski and Reutebuch)A recent study by RSAC and PNW reports on the known lidar applications / studies in the USFSMore detail and full report at
18Lidar Mission Specifications Wide lidar usage (in resource mapping) is just in its infancyLike aerial photos – specifications are linked to information requirementsCurrently no industry standards for specific applications2 Areas to specifyAcquisition specsProcessing and Delivery specsGovernmentVendorSpecsQA / QCSetting specifications for lidar data acquisitions are not available as “boilerplate” for contracting …1st step is to clearly understand and articulate (better yet write)Experiences of research and pilot projects – and other agencies – can be used as guidance
19Lidar Specifications – Acquisition Acquisition SpecificationsPoint density (post spacing)DTM -> based on vertical accuracy requirementsVegetation Applications1.5 point per square meter absolute minimum4-6 points per square meter are preferableSpecify whether collected leaf on or leaf offMultiple returns per pulseMaximum 15-degree off nadir scan angle unfiltered dataFlight lines should have 50% “side lap” (30% minimum)Cross flights for calibrationAttributes delivered: X, Y, Z, Intensity, Scan Angle, Return #High resolution digital imagery (if possible)Acquisition Specifications1.5 point per square meter absolute minimum; 2-4 points per square meter are preferable (note: ask the vendor specify nominal point density, not "contour intervals")Multiple returns per pulse (typically a maximum of 4; you want more than just first and last return lidar) – required if you need vegetation structure information (more than just top of canopy)you may want to specify whether the lidar is collected leaf on or leaf off, depending on mission objectives … often leaf off in hardwood systemsSidelap allows a more detailed analysis of the sub-top of canopy structure because you can look into the treesmaximum of 15-degree off nadir scan angle unfiltered data (i.e., unfiltered for ground returns) should be delivered in LAS formatone or more cross flights for calibration vertical and horizontal accuracy specification should be provided by vendor (typically ~15-cm vertical, 30-cm horizontal w/95% CI)attributes in LAS file should be X, Y, Z, Intensity, Scan Angle, Return Number, and [Optional: GPS Time]
20Lidar Specifications – Processing and Delivery Vendor Processing and Delivery SpecificationsLidar data delivered in overlapping tilesGIS dataset of the tiling systemGIS dataset of the flight linesReport on GPS ground station locationsGeographic projection information (including vertical datum)Heights should be orthometric heightsReport that lists all files deliveredOptional:Tiled points filtered for bare earth returnsA high resolution DTMVendor Processing and Delivery Specificationslidar data should be tiled into practical units, often 2-km x 2-km; a GIS dataset of the tiling system should be includedlidar data should be delivered with a GIS dataset of the flight lines used to collect the data, typical overlap is about 30%a report on what GPS ground station locations were used to reference the dataall geographic projection information should be included; heights should be orthometric heightsa list of all files delivered to verify contract performance and full deliveryyou may want to specify whether the lidar is collected leaf on or leaf off, depending on mission objectives[Optional: Tiled points that have been filtered for bare earth returns][Optional: A high resolution digital terrain model (1-m or 2-m resolution)][Optional: High resolution photography (or digital equivalent) is a very valuable addition to the lidar data and can often be acquired at the same time]
21Approximate Costs of Acquisition Mobilization$8k – $15kAdministrationProject and flight planningWeather contingencyPre-collection tasksBasic Data Collection and Post-processingDepends on study area size ($0.50 -$2.50/acre for 1M – 15k acres)~$1/acre for a 250K acre projectRaw lidar dataBare earthFirst surfaceThese figures are presented very hesitantly … it is a dynamic marketOne downside of lidar data is it’s relatively high cost. This too is changing, however.Costs are a function of how much area is to be collected … and more so on the derived products you want the vendor to provide. Note that the third level of processing (above, Generating GIS Data Sets) is only available from a very limited number of vendors and are by no means standard products.Lidar data consortiums are being created to collect lidar data over entire states –Carolinas, Wyoming, Nevada?, Washington?The image shows the progression from raw lidar points (top), to bare earth DTM (middle), to lidar points that are normalized based on the DTM … this changes the color scheme and you can see tall trees in the front and right of the image that were not visualizeable without the normalization.Advanced ProcessingAdditional $3 – $7/acreCanopy coverTree heightForest biomassOther vegetation derivatives
22Summary Lidar is an exciting (relatively) new technology Provides measurements!Vegetation structural information are its strengthsExisting research provides a strong foundationLidar processing requires special skills/toolsData volume can be an issueSpecialized software (not just ESRI products) required for efficient large scale analysisLidar missionsSpecifications becoming better understoodStill expensive, but costs coming downMultiple resource applications & consortia allow for cost sharing