Aerial and Terrestrial Remote Sensing

Flatirons, Inc. remote sensing services include UAS photogrammetry, UAS LiDAR collection and processing, terrestrial LiDAR collection and processing, and aerial imagery acquisition including oblique and video capture. All of our aerial collection capabilities incorporate the use of drone mounted photogrammetric mapping cameras and LiDAR sensors. Our UAS pilots are licensed Part 107 through the FAA which is the legal framework for drone pilots. Additionally (and equally important), our drone pilots are licensed professional surveyors, geospatial analysts, and GISP certified professionals with the experience of collecting and delivering accurate 2D and 3D mapping products. The combination of professional land surveyors coupled with experienced GIS professionals fills a niche that combines remote sensing, surveying, and GIS. Flatirons, Inc. has the capabilities to provide mapping products in a variety of outputs that meet or beat conventional surveying standards.

Flatirons surveyors and drone pilots work in tandem together as the mission is the same - to collect data used for mapping, land surveying, and GIS purposes. Remote sensing is a product of surveying, albeit from another platform. The end result of remote sensing and land surveying are similar, especially as it applies to topographic mapping where mapping landforms and feature collection are paramount. With the addition of UAS remote sensing, we are able to provide mapping products from both ground-based collection as well as from aerial platforms. Where drone LiDAR collection might not be possible in areas due to restricted airspace, Flatirons, Inc. is capable of using ground-based collection methods to acquire topographic data. It is essential to have experienced land surveyors working hand in hand with geospatial professionals and drone pilots, as their shared goal is to provide high quality and highly accurate 2D and 3D mapping products.

All of our aerial mapping missions incorporate the use of ground control point targets (GCP's), which are used to enhance vertical and horizontal accuracies during the image processing phase. GCP's are also used as check points, helping to ensure the mapping meets accuracy requirements established by the American Society of Photogrammetry and Remote Sensing (ASPRS). Due to certain factors inherent to drone based remote sensing, such as the instability of the platform due to wind, obstacles in the line of sight, and other environmental factors, achieving consistently high accuracy can be difficult. Through our methodology and professional standards, Flatirons, Inc. is able to meet or exceed Standard Mapping and GIS Work accuracies as defined by ASPRS. The accompanying slide shows ground control points being collected by a land surveyor using a rover GPS connected to an RTK base station. As stated before, it absolutely essential that aerial remote sensing products integrate the use of GCP's for QC and processing. This is where land surveying meets drone remote sensing...it starts with quality ground control. Always.

Photogrammetric mapping is the art and science of extracting data from aerial photography. Of the many types of aerial mapping that exist, Flatirons, Inc. specializes in producing orthomosaic datasets from captured aerial images using ground control points in the image processing. An orthomosaic, by definition, is a composite of aerial images that have been stitched together with the distortion removed from the final image dataset. The result of the processing is one massive image where features are geometrically and spatially correct. The orthomosaic is a pixelated 2D product (raster) where pixel sizes are determined before the flight mission has begun. In terms of pixel sizes in the orthomosaic, there are several factors that determine the ground sample distance (GSD) in the imagery, including flying height and camera specifications. For example, the orthomosaic shown in the adjoining slide was flown at 400 feet above ground level (AGL) with a ground sample distance of 1.52cm or a 1.52cm pixel resolution. In other words, the pixel size in the orthomosaic represents the same distance on the ground...or one 1.52cm pixel in the orthomosaic represents 1.52cm on the ground. When including ground control points in the processing while maintaining a flying height of 400 feet (or lower) with an adequate photogrammetric mapping camera, the results are impressive. Along with high resolution imagery comes the remainder of the products that can be derived from photogrammeteric mapping, including orthomosaics, digital terrain models (DTM, bare earth models), digital surface models (DSM, bare earth including everything above ground), 3D mesh scenes, and contours.

This slide shows a UAS and camera being prepared and assembled for imagery collection. The drone will contain a pre-programmed flight plan using flight speed, sensor focal length, flying height, and other factors to build a plan that will capture the imagery of a defined area. The goal of the mission will be to produce 2D and 3D photogrammetric mapping products that will aid land surveying deliverables to include CAD based products and remote sensing items. The aerial images will contain coordinates (geotagged) from the drone's onboard GPS receivers thus making the imagery georeferenced.

This slide provides an example of an orthomosaic 3D scene tilted at an angle which offers another view of the imagery from a perspective other than top down. With proper software, one can tilt and turn an orthomosaic at multiple angles for different viewing perspectives.

Similar to photogrammetry, LiDAR collection can be obtained by using UAS methods, manned aircraft, and/or terrestrial laser scanning (TLS). This topic will include LiDAR acquisition using drone (UAS) collection methods as it pertains to topographic mapping. While photogrammetric mapping is considered passive data collection, LiDAR collection is considered active as the sensor emits swaths of light that bounce back from the intended target (ground, vegetation, etc) to the sensor. The LiDAR sensor uses the time it took for each pulse to return to the sensor to calculate the distance traveled. Once the data from a LiDAR sensor has been processed, a 3D model known as a point cloud is produced. Where LiDAR is collected using a drone with a GPS receiver, the LiDAR is considered georeferenced to the earth's surface using coordinates derived from the GPS. Post processing using accurate GPS data will tighten the LiDAR's accuracies even further. The accompanying slide shows a LiDAR point cloud that has been processed and displayed in processing software. Notice the bare earth features as well as vegetation and power lines shown. Where aerial photogrammetry uses photographs to display features, LiDAR, as mentioned above, uses point clouds. This point cloud was captured using UAS technology and LiDAR scanner.

This video provides an example of a Flatirons, Inc. LiDAR scanner that is mounted onto a UAS at the beginning of a collection mission. Pre-configuring the mission using a suitable flying height and flight speed will ensure proper collection of the LiDAR point cloud. Using drone mounted GPS, the LiDAR will acquire coordinates from the GPS and georeference to a known coordinate system. Post-processing of the LiDAR data uses information from OPUS (Online Positioning User Service) for enhanced vertical and horizontal accuracies.

The accompanying image shows the combination of photogrammetry and LiDAR. The orthomosaic was constructed using drone captured imagery while the contours were derived from drone captured LiDAR. While digital terrain models (DTM) and contours can be built photogrammetrically from aerial photography, more accurate bare earth models and contours are built from surfaces derived from LiDAR point clouds. Using both forms of data from photogrammetry and LiDAR provide a good model of the earth's surface and it's features.

The adherence to accuracy standards cannot be stressed enough in Flatirons mapping deliverables. It is of utmost importance that we provide quality, accurate mapping products to our customers including remotely sensed 2D and 3D data products. Accuracy in photogrammetric and LiDAR mapping begins with ground control points (GCP's). Following the American Society for Photogrammetry and Remote Sensing accuracy standards, Flatirons, Inc. strives to maintain accuracies in the Standard Mapping and GIS Work. The adjoining slide shows a surveyed target with red cross within 1 centimeter of the target shown in the orthomosiac. This consitutes the highest level of accuracy according to ASPRS standards for Highest Accuracy Work. As previously mentioned, it is difficult to consistently meet the highest level of accuracies due to environmental factors affecting the drone. You can count on Flatirons, Inc. to work diligently to meet or exceed Standard Mapping and GIS Work accuracy.

Terrestrial Laser Scanning (TLS) is a technique that is used for collecting point clouds using ground-based collection. This type of collection is called SLAM (simultaneous location and mapping) and is used in GPS denied environments such as tunnels, mine shafts, and certain structures. TLS is a suitable method for collecting as-built data for features that cannot be collected using GPS/RTK surveying methods. Items such as volumetric calculations, size dimensions, and change detection can be extracted from terrestrial scanning. The accompanying slide shows a terrestrial LiDAR scan of a stormwater containment vault that will be used to extract as-built information.

With most high-quality terrestrial scanners, on the fly viewing of captured data ensures the data collection is going smoothly. Field crews are able to verify accuracy of data, and that no objects were missed prior to returning the data to the office for post-processing and analysis. This slide shows the collection of an underground stormwater containment vault which will be used for as-built purposes.

For construction management purposes, drone oblique shots (angled) and video allow project managers and stakeholders the opportunity to monitor construction progress from remote locations, including their offices or anywhere that has an internet connection. Monthly or bi-weekly image and video captures allow for ascertainment of progress throughout the life of the project. Specific parts of a project can be collected for inspection purposes as well.

Another shot of a construction site using high-resolution/high-definition UAS aerial photography showing heavy equipment in operation. Construction managers have the ability to view the progress of the building being constructed using before, during, and after construction photography and video. Specific timelines of construction can be monitored as each image and video that is collected contains a time stamp. Another aspect of using UAS remote sensing for construction management includes stockpile and mass grading monitoring throughout the entirety of the project.