2023 NOAA NGS Lidar DEM: Long Island Sound, NY

NOAA Long Island Sound Topobathymetric Lidar data were collected by NV5 using Leica Chiroptera/Hawkeye 4X and Chiroptera/Hawkeye 5 systems in four blocks. Block01 was flown between 20230305 and 20230411 in 14 missions, block02 was flown between 20230305 and 20230722 in 23 missions, block03 was flown between 20230316 and 20231028 in 13 missions and block04 was flown between 20230410 and 20230530 in 19 missions.

The final classified lidar data were then transformed from ellipsoid (GRS80) to orthometric height (Geoid18) and used to create topobathymetric DEMs in Cloud Optimized GeoTIFF format with 1m pixel resolution.

This lidar data was required by National Oceanic and Atmospheric Administration (NOAA) and the National Geodetic Survey (NGS), Remote Sensing Division Coastal Mapping Program (CMP) to enable accurate and consistent measurement of the national shoreline. The CMP works to provide a regularly updated and consistent national shoreline to define America's marine territorial limits and manage coastal resources.

The NOAA Long Island Sound Topobathymetric Lidar block datasets include all lidar returns. An automated grounding classification algorithm was used to determine bare earth and submerged topography point classification. The automated grounding was followed with manual editing. Classes 2 (ground), 40 (submerged topography), and 43 (submerged object) were used to create the final DEMs. The full workflow used for this project is documented in the NOAA Long Island Sound Topobathymetric Lidar final report.

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the National Geodetic Survey, the Office for Coastal Management, or its partners.

Block01

Block02

Block03

Block04

Data is available online for bulk and custom downloads.

None

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

OS Independent

Lidar horizontal accuracy is a function of Global Navigation Satellite System (GNSS) derived positional error, flying altitude, and INS derived attitude error. The obtained RMSEr value is multiplied by a conversion factor of 1.7308 to yield the horizontal component of the National Standards for Spatial Data Accuracy (NSSDA) reporting standard where a theoretical point will fall within the obtained radius 95 percent of the time (ACCr). The project specification requires horizontal positions to be accurate to 1.0m(RMSE).

Block01, Block02 and Block03:

Based on a flying altitude of 400 meters, an IMU error of 0.003 decimal degrees, and a GNSS positional error of 0.008 meters, the RMSEr value for the Leica Chiroptera shallow green and NIR sensor data is 0.038 meters, with a ACCr of 0.07 meters at the 95% confidence level.

The RMSEr value for the Leica Hawkeye deep green sensor data is 0.038 meters, with a ACCr of 0.07 meters at the 95% confidence level based on a flying altitude of 400 meters, an IMU error of 0.003 decimal degrees, and a GNSS positional error of 0.008 meters.

Block04:

Based on a flying altitude of 400 meters, an IMU error of 0.003 decimal degrees, and a GNSS positional error of 0.008 meters, the RMSEr value for the Leica Chiroptera shallow green and NIR sensor data for Block04 is 0.038 meters, with a ACCr of 0.07 meters at the 95% confidence level.

The RMSEr value for the Leica Hawkeye deep green sensor data in Block04 is 0.051 meters, with a ACCr of 0.09 meters at the 95% confidence level based on a flying altitude of 400 meters, an IMU error of 0.004 decimal degrees, and a GNSS positional error of 0.008 meters.

Please refer to the NOAA Long Island Sound Topobathymetric Lidar final data report for final accuracies.

Absolute accuracy was assessed using both Non-Vegetated Vertical Accuracy (NVA) and Vegetated Vertical Accuracy (VVA) survey methods. Survey checkpoints were evenly distributed as feasible throughout the project area. NVA compares known ground check point data that were withheld from the calibration and post-processing of the lidar point cloud to the derived gridded bare earth DEM. NVA is a measure of the accuracy of lidar point data in open areas with level slope (less than 20°) where the lidar system has a high probability of measuring the ground surface and is evaluated at the 95% confidence interval (1.96*RMSE). Project specifications require NVA meet 0.196 m accuracy at the 95% confidence interval. Ground check points located in land cover categories other than bare earth or urban were used to compute the Vegetated Vertical Accuracy (VVA). Project specifications require VVA meet 0.294 m based on the 95th percentile tested against the derived bare earth DEM. Please refer to the NOAA Long Island Sound Topobathymetric Lidar final data report for final accuracies.

Block01:

The Block01 dataset Non-Vegetated Vertical Accuracy tested 0.058 m vertical accuracy at 95% confidence level against the derived bare earth DEM in open terrain using 13 ground check points, based on RMSEz (0.030 m) x 1.9600. The Vegetated Vertical Accuracy tested 0.108 m vertical accuracy at the 95th percentile against the derived bare earth DEM using 11 landclass points.

Block02:

The Block02 area dataset Non-Vegetated Vertical Accuracy tested 0.057 m vertical accuracy at 95% confidence level against the derived bare earth DEM in open terrain using 16 ground check points, based on RMSEz (0.029 m) x 1.9600. The Vegetated Vertical Accuracy tested 0.111 m vertical accuracy at the 95th percentile against the derived bare earth DEM using 10 landclass points.

Block03:

The Block03 area dataset Non-Vegetated Vertical Accuracy tested 0.049 m vertical accuracy at 95% confidence level against the derived bare earth DEM in open terrain using 5 ground check points, based on RMSEz (0.025 m) x 1.9600. The Vegetated Vertical Accuracy tested 0.158 m vertical accuracy at the 95th percentile against the derived bare earth DEM using 5 landclass points.

Block04: The Block04 area dataset Non-Vegetated Vertical Accuracy tested 0.060 m vertical accuracy at 95% confidence level against the derived bare earth DEM in open terrain using 10 ground check points, based on RMSEz (0.031 m) x 1.9600. The Vegetated Vertical Accuracy tested 0.461 m vertical accuracy at the 95th percentile against the derived bare earth DEM using 6 landclass points.

Data is backed up to tape and to cloud storage.