LIDAR data, Gulf of Carpentaria

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Link to the data In August/September 2017, small footprint discrete return airborne LIDAR data were acquired alongside digital aerial imagery along a nominal 1 km strip along the coastline of the Gulf of Carpentaria that extended from Groote Eylandt, NT through to Weipa, QLD. The acquisitions focused on mangrove areas, including those that experienced dieback in 2015/16 but were not biased towards these areas. To achieve large comprehensive coverage of the coastal strips, multiple parallel flightlines were flown. At the Leichhardt River mouth, a 21-flightline grid was flown. This dataset consists of:

a) Point clouds in the form of .las 1.2 files with decomposed discrete returns and intensity and all fields populated delivered as 1 km x 1 km tiles and/or strips along the coast. b) Digital terrain models (DTMs) at 1m spatial resolution and canopy height models (CHMs) at 0.5 m spatial resolution. The raw data are available through the TERN data portal and directly from Airborne Research Australia (ARA). The list and details of the CHMs and DTMs derived from the tiled data is given in the section ‘File Attributes’. Georeferencing and other information on image dimensions of the files are provided in the section on Spatial and Temporal extents.

Abstract or Summary To establish a baseline of mangrove extent and structure along the Gulf of Carpentaria, northern Australia, a consortium consisting of Airborne Research Australia, Queensland Herbarium, Charles Darwin University, The National Environmental Science Program (NESP) supported by TERN AusCover and the University of New South Wales (UNSW) coordinated the acquisition of digital aerial imagery and airborne LIDAR along a coastal strip extending from Weipa (Queensland) to Groote Eylandt (Northern Territory). The acquisitions were largely in response to the mangrove dieback event in 2015/2016, which affected large sections along the Gulf of Carpentaria coastline as well as other areas in northern Australia. The LIDAR data were acquired alongside digital aerial photography along a nominal 1 km strip although, for most areas, several parallel flights were conducted with this increasing the area of overlap. In others, multiple overpasses were flown, including inland from the coast along river estuaries. Over 7000 km of flightlines were flown with a NPS exceeding 0.5 m along the majority of the flightlines and often < 0.3 m. The LIDAR dataset was acquired alongside digital aerial photography and all data are freely available through TERN AusCover.

Data quality During the flights, efforts were made to fly at low tide and during the middle of the day to avoid variations in solar illumination. Cloud-free conditions were experienced during most of the flights although winds were strong over some areas. This could not be determined until the mission was underway and was planned on a day-by-day basis. 

The absolute vertical accuracy is ± 0.20 m at 1σ and represents the uncertainty of a measured elevation compared to the true elevation with respect to the established datum. Elevation datum is AHD using the AUSGeoid09 model. The relative vertical accuracy is ± 0.10 m at 2σ, which is the uncertainty of the measured elevation of one point with respect to another point (point-to-point accuracy) within and across adjacent flight lines. 
The absolute horizontal accuracy is ±0.30 m at 1σ. The IMU unit/INS system met the flight limit specifications1 recommended by 
ASPRS , namely ≤ 0.005o for roll; ≤ 0.005o for pitch; and ≤ 0.008o for heading (i.e. yaw). 
 During the overflights, GPS base stations could not be deployed because of the remoteness of the area surveyed and the large distances covered. The Nominal Pulse Spacing (NPS), which is detailed in the USGS base LIDAR Specification, is the spacing between points in the collection when in reference to single instrument, single swath, first return only LIDAR point data and is usually predicted by the system manufacturer’s flight planning software to indicate the “grid” spacing of the collected points based upon the input flight plan parameters. Limiting the points being considered to those that are first return only, and from a single flight pass, the NPS is calculated using:

NPS= 1/√Density

The point densities were primarily > 4 pts per m2 (0.5 m NPS) but were as high as 20 pts per m2 (0.22 m NPS). The processing of the LIDAR was undertaken to cover the absolute maximum area and hence data acquired in the turns and associated with the edges of the LIDAR swath are also included in the dataset. No attempt has been made to strip align parallel flightlines. In all cases, the data have been provided such that adjustments can be undertaken by the users.