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Benefits of High-Performance GPS/IMU

Headwall’s High-Performance GPS/IMU, coupled with software that uses Post-Processing Kinematics (PPK), a GPS correction technique that corrects location data after drone data has been captured and downloaded, significantly reduces image distortions and enables more accurate orthomosaicking of multiple flight swath images.
Here are point-cloud images taken from otherwise identical Headwall airborne hyperspectral imaging platforms with LiDAR. The point-cloud image on the left was taken using the Legacy (Gen 2) GPS/IMU. The point-cloud image on the right was taken with the High-Performance GPS/IMU. Point-cloud data was visualized using the opensource program CloudCompare1, with coordinates exported to scalar fields and the display range for height (Z) made as close to identical as possible.

Benefits of High-Performance GPS/IMU

Plus LiDAR Systems and Software

 

GPS/IMU ACCURACY AFFECTS LIDAR DATA CAPTURE AND VISUALIZATION

The more accurate and precise your positioning data, the less distortion you will see in your hyperspectral images and LiDAR point clouds. When utilizing otherwise identical airborne platforms, the quality of the point-cloud data captured from integrated LiDAR systems differs due to employing either the Legacy (Gen 2) or High- Performance GPS/IMU.

Headwall now only sells the High-Performance GPS/IMU for LiDAR-equipped systems. Note the clarity of the point-cloud image on the right, captured on a Headwall unmanned aerial vehicle (UAV) system equipped with the High-Performance GPS/IMU, versus the image on the left, captured on a system equipped with the Legacy (Gen 2) GPS/IMU.

Here are point-cloud images taken from otherwise identical Headwall airborne hyperspectral imaging platforms with LiDAR. The point-cloud image on the left was taken using the Legacy (Gen 2) GPS/IMU. The point-cloud image on the right was taken with the High-Performance GPS/IMU. Point-cloud data was visualized using the opensource program CloudCompare1, with coordinates exported to scalar fields and the display range for height (Z) made as close to identical as possible.
Figure 1. Here are point-cloud images taken from otherwise identical Headwall airborne hyperspectral imaging platforms with LiDAR. The point-cloud image on the left was taken using the Legacy (Gen 2) GPS/IMU. The point-cloud image on the right was taken with the High-Performance GPS/IMU. Point-cloud data was visualized using the open-source program CloudCompare (1), with coordinates exported to scalar fields and the display range for height (Z) made as close to identical as possible (red = high, blue = low).
Figure 2. Multiple flight swaths were orthorectified and stitched together in the above images, left using the Legacy (Gen 1) GPS/IMU and right using the High-Performance GPS/IMU. Notice the image distortions of the parking lot lines and the reflectance tarp with standard GPS/IMU data. The Legacy (Gen 1) GPS/IMU system had a single GPS antenna, and at speeds below 10 meters per second, the resulting ortho-mosaicked images can be inferior to those produced using the High-Performance GPS/IMU.

GPS/IMU ACCURACY AFFECTS ORTHORECTIFICATION AND ORTHOMOSAICKING

In addition to affecting LiDAR data, inaccuracies in GPS/IMU data result in image distortions that impact the ortho-mosaicking of flight-swath images, as shown in Figure 2.

Headwall’s High-Performance GPS/IMU coupled with software that uses Post-Processing Kinematics (PPK), a GPS correction technique that corrects location data after drone data has been captured and downloaded, significantly reduces image distortions and enables more accurate orthomosaicking of multiple flight swath images.

The Headwall Legacy (Gen 2) GPS/IMU can be distinguished from the Legacy (Gen 1) GPS/IMU, by the presence of two antennae on the Gen 2 model, versus a single antenna on the Gen 1 model. Neither of the Legacy models have GPS post-processing implemented, as the High-Performance GPS/IMU has (using PPK).

AVAILABLE SMART TARGET BASE STATION

Headwall portable base stations enable PPK anywhere a GPS signal is available. Data can be downloaded 1 to 2 hours after flight versus waiting 24 hours or more when relying on National Geodetic Survey (NGS) Continuously Operating Reference Stations (CORS) data. Contact Headwall or your local authorized reseller for more information about our Smart Target Base Stations, as well as other techniques to maximize the accuracy and precision of your positioning system.

LIDAR SYSTEMS AND SOFTWARE FOR GENERATING DEMS AND 3D TERRAIN DATA

  • Integrated hyperspectral and LiDAR payload and turnkey systems
  • Capture point-cloud and hyperspectral data simultaneously
  • Dual returns for better canopy characterization
  • Boresighted with GPS for extremely precise positioning
  • Headwall LiDAR ToolsTM generates high resolution .LAS and Digital Elevation Model (DEM) files
  • Significantly less overlap required than photogrammetry
  • Designed for use with the High-Performance GPS
Figure 3. Two-dimensional image created from a DEM file saved by LiDAR Tools from the LiDAR point cloud captured during a flight over a commercial office park.
Figure 3. Two-dimensional image created from a DEM file saved by LiDAR Tools from the LiDAR point cloud captured during a flight over a commercial office park.

AIRBORNE HYPERSPECTRAL IMAGING AND LIDAR: COMPLEMENTARY SYSTEMS

Hyperspectral imaging and light detection and ranging (LiDAR) are very much complementary. Hyperspectral imaging can remotely detect conditions such as crop disease, water deficits, or plant stress or vigor, while LiDAR measures distances with extreme precision using pulses of laser light. When combined with accurate positioning data from a global positioning system and inertial measurement unit (GPS/IMU) LiDAR data can be used to produce an extremely accurate digital elevation model (DEM) of terrain.

 

LiDAR Tools™ software comes with each LiDAR-equipped payload package from Headwall. These systems, such as the Hyperspec® Co-Aligned HP VNIR-SWIR sensor or Nano-HP® VNIR sensor, are mounted to compatible, lightweight drones, providing flight-ready operation, and represent the gold standard for lightweight remote sensing airborne platforms. Adding LiDAR only contributes 0.8kg to the imaging payload weight.

 

The combination of hyperspectral imaging and LiDAR is especially powerful because the entire dataset can be acquired simultaneously,
maximizing efficiency by minimizing flight time. Requirements for overlap of adjacent flight paths are also significantly less than those for photogrammetry. The DEM file that the LiDAR Tools software provides is utilized in the process of orthorectification of the hyperspectral imaging data.

The top image was produced by orthorectifying a hyperspectral imaging swath taken by a Headwall UAV using 30-meter resolution USGS DEM data, while the bottom image was produced by orthorectifying the same hyperspectral imaging swath using 10- cm resolution DEM data obtained using the integrated LiDAR. Notice the distortions in the top image created using the 30-meter DEM data, which are absent in the bottom image.
Figure 4. The top image was produced by orthorectifying a hyperspectral imaging swath taken by a Headwall UAV using 30-meter resolution USGS DEM data, while the bottom image was produced by orthorectifying the same hyperspectral imaging swath using 10- cm resolution DEM data obtained using the integrated LiDAR. Notice the distortions in the top image created using the 30-meter DEM data, which are absent in the bottom image.

Headwall’s focus is integrating multiple sensor modalities and providing the tools necessary for the most efficient and productive workflow for data exploitation. Customers benefit from our expertise in the capture and interpretation of data from our robust and proven platforms, whether imaging payload systems added to a UAV or an entire turnkey integrated solution including imaging and positioning packages
and the UAV itself.

 

LiDAR ToolsTM software comes with every integrated airborne system with LiDAR sold by Headwall. The software runs on contemporary 64-bit Windows operating systems, and allows saving of LiDAR .LAS files, as well as digital elevation model (DEM) files. Inaccurate DEM data will cause errors in magnification and geolocation, since the distance from the sensor to the object sets magnification. Although DEM data from the US Geological Survey (USGS) can be obtained for free, it is typically limited to resolutions as coarse as 30-meters in remote locations. Outside of the United States, accurate DEM data may have a high cost associated with it or may not be available at all.

 

The ability to fly a UAV at will (presuming weather conditions are favorable) to obtain high-resolution DEM data can make a tremendous difference in accuracy, and produce images of strikingly high quality. See the comparison images above.

Headwall LiDAR Tools pixel-level fusion of hyperspectral and LiDAR data overlaid onto 3D terrain using third-party software. (RED = steep features, e.g. cliffs and trees; GREEN & BLUE = difference between vegetation and ground). Image courtesy BeamIO.
Figure 5. Headwall LiDAR Tools pixel-level fusion of hyperspectral and LiDAR data overlaid onto 3D terrain using third-party software. (RED = steep features, e.g. cliffs and trees; GREEN & BLUE = difference between vegetation and ground). Image courtesy BeamIO.
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