Windstorm Simulation & Modeling Project

Transcription

1 Windstorm Simulation & Modeling Project Broward County Digital Elevation Models Interim Report Prepared for: The Broward County Commission Emergency Management Division 201 N. W. 84 Avenue Plantation, FL Florida International University International Hurricane Center West Flagler Street EAS 2710 Miami, FL (305) September 19, 2001

2 Executive Summary The following is an interim report describing acquisition parameters, coverage areas and results of preliminary testing as part of the Windstorm Simulation & Modeling Project per the contract agreement established March 8, 2001 between, Florida International University International Hurricane Center (IHC) and Broward County. On July and August 6-7, an Optech Airborne Laser Terrain Mapper (ALTM) 1210 LIght Detection And Ranging (LIDAR) mapping system mounted in a Cessna 337 aircraft was used to collect topographic data in Broward County. Data was collected at a nominal altitude of 1100 m (3600 feet) with the survey consisting of 128 overlapping 600-m-wide swaths. Ground control was provided by 3 Ashtech Z-12 GPS receivers equipped with choke ring antennas. The total coverage of low-lying areas exceeded 110,000 acres and included all areas depicted in Figure 1. Over 100 million irregularly spaced ground surface elevations were measured with a nominal point spacing of 2.5 m (8.2 feet). Preliminary error analysis yielded excellent results. Initial review of the data depicted complete and accurate data sets, revealing no foreseeable problems with future data processing. Figure 1. Area of data acquisition (blue) for Broward County and 1999 Broward County LIDAR study area (gray). Project:

3 Introduction In , The International Hurricane Center (IHC) was awarded grant funding by Federal Emergency Management Division (FEMA) and the Florida Department of Community Affairs (FLDCA), for a program entitled the Windstorm Simulation and Modeling project. Four tasks under this three year project included 1) the re-evaluation of existing storm surge models including SLOSH, CMEPS and TAOS, 2) data acquisition of high-resolution elevation data via LIDAR technology for participating South Florida counties 3) computer simulation of findings for researchers and the general public and 4) development of public awareness and education programs in regards to human vulnerabilities to hurricanes and the means to mitigate the risks. This project is also supported partially from matching funds provided from participating counties including Broward, Miami-Dade, Palm Beach, and Monroe Counties. On March 8, 2001, Broward County and the IHC reached a final contract agreement about participating in this project and as part, use Airborne Laser Terrain Mapper (ALTM) technology for their evacuation zone revision project. Following this agreement initial field reconnaissance was conducted, base stations were established, and the ALTM system was used to collect detailed topographic data in Broward County in July and August This report describes field procedures, data acquisition, preliminary processing, and the results of preliminary error analysis. Establishment of Base Stations The establishment of base stations is needed for LIDAR data collection and processing. Survey monuments were High Accuracy Reference Network (HARN) stations, other 1 st order vertical accuracy National Geodetic Survey (NGS) benchmarks, or Broward County primary control network stations. The accuracy of published control stations was checked. The IHC collected at least three five-hour static GPS data sets for each control station. The collected GPS data was differenced from local Miami Continuously Operating Reference Stations (CORS). Poorly collected GPS data was identified and discarded. Good data were averaged to produce a position for each control site. Data Acquisition The goal of this project was to acquire data in all areas of Broward County that could possibly be affected by storm surge. In 1999, a similar project was conducted where all areas east of I-95 were collected. This project covered areas west of I-95, as shown in Figure 1. The original flight plan consisted of 124 N-S trending spaced 500 m apart and 4 E-W trending swaths near the Ft. Lauderdale Airport. In order to maximize coverage area per flight pass while maintaining data quality, the following acquisition parameters were planned: height above ground angle, 1100m; ground speed, 191 km/hr (100 Knots); scan angle (FOV), ±15 ; scan rate of 21 Hz; a pulse rate,10khz. These parameters produce a 650-meter-wide swath of 30 cm wide laser footprints spaced approximately every 2.5 beneath the flight path. A schematic diagram of the nominal acquisition parameters used in this project is shown in Figure 2. Project:

4 Figure 2. Schematic diagram showing data acquisition parameters used for Broward County ALTM survey. Data was collected on seven separate days. In order to insure quality GPS data, flight schedules were planned to coincide with periods of low Position Dilution of Precision (PDOP). The system was initially deployed during night hours on July 13-17, 2001 and data for both Broward County and Palm Beach County was collected. The system was re-deployed on August 6 and 7, 2001 to survey areas not covered and to fill in data gaps found during initial processing of the July data. Due to clouds and air space restrictions, flight heights varied between 700 and 1200 m. The scan angle and frequency were adjusted as necessary to maintain a 600 m-wide swath and a nominal 2.5 m point spacing. Each deployment typically took 4-5 hours during which GPS data was continuously recorded on both the aircraft and on the 2-3 stations on the ground. A detailed log of all flight and derived ground spacing parameters is given in Appendix A. For both Broward and Palm Beach Counties a total of 124 N-S trending swaths and 4 E-W trending swaths were collected (Figure 3). In total, the project measured over 140 million irregularly spaced ground elevations. Project:

5 Figure 3. Index map of eastern Broward County showing separate days of data collection (colored lines), GPS ground stations (Red Stars), and the 1999 Eastern Broward County LIDAR Study Area (gray). Ground GPS data were recorded at 1 sample per second by Ashtech Z-12 receivers equipped with choke ring antennas and operated by FIU staff and graduate students. The GPS antennas were fixed atop 2-meter-high fixed height tripods placed over previously surveyed monuments. All deployments utilized at least two independent ground stations. Details and coordinates of the GPS ground control station locations are given in Appendix B. Preliminary Data Processing After each flight, LIDAR and GPS data are downloaded to a computer and processed by the Optech/Topscan proprietary software. Operation of this software proceeds in several steps. First, ground station coordinate information is entered and the aircraft and ground station GPS data are differentially processed to produce a kinematic aircraft trajectory. The trajectory information is combined with the range, scan, and IMU data to produce laser return coordinates. Output consists of 9 column ASCII text files containing the UTM zone 17 eastings and northings, the ellipsoidal heights, and the return intensity for both the first and last laser detection for each pulse. We replaced the Optech/Topscan proprietary software trajectory with one computed using the NGS Kinematic and Rapid Static (KARS) program. This program uses both L1 and L2 carrier Project:

6 phase data as well as precise satellite ephemeris. Dr. Gerry Mader of NGS computed the KARS trajectories for this project through a consulting agreement with FIU. Preliminary Error Analysis The root mean square error (RMSE) provides a convenient means to quantitatively estimate the error in a set of measurements. The National Standard for Spatial Data Accuracy (NSSDA) defines the RMSE to be the square root of the average of the squared differences between dataset coordinate values and coordinate values from an independent source of higher accuracy (Federal Geographic Data Committee, 1998). For a DEM, the vertical error, RMSE z is defined as RMSE z = ( z z ) t, i n 2 m, i where z t,i is the elevation of the ith test point, z m,i is the interpolated DEM elevation at the test point, and n is the number of test points. NSSDA recommends using a minimum of 20 test points distributed over the geographic area of interest. Accuracy is reported in measurement units at the 95% confidence level. A 95% confidence level means that 95% of the measurements will have an error of less than or equal to the reported accuracy. If the error is normally distributed with zero mean, the 95% vertical accuracy is equal to 1.96 times the RMSE z. Preliminary error analysis was conducted at a few sites in Broward and Palm Beach County. Both counties were flown simultaneously, thus calibration of data for each county is equivalent. Figure 4 shows groundtruth data near Pioneer Park in Deerfield Beach. The groundtruth data was collected using a rapid static GPS system. The GPS data was processed using Ashtech AOS software to produce points. The points represented a ground profile of NE 2 nd Street in Deerfield Beach as seen in Figure 5. The profile was differenced to the LIDAR data profile at the same location. Mean difference, standard deviation, and RMSE values were calculated and plotted on the figure. Figures 6 and 7 show groundtruth data provided by Palm Beach County Engineers. North south and east west transects were extracted and differenced to the LIDAR data profile at the same location. Mean difference, standard deviation, and RMSE values were calculated and plotted on the figures. Preliminary RMSE values for all sites are less than 20 cm. Figures 4, bottom of 6, and 7 show RMSE values of less than 11 cm and as good as 4 cm. Future filtering of the LIDAR data should improve RMSE values, and further investigation of the Lantana and Congress intersection is planned to identify the relatively large RMSE value. Project:

7 Groundtruth Data at Groundstation Pioneer Groundtruthing Profile Groundtruthing Points Gridded LIDAR Profile Mean Difference (m) = Standard Deviation (m) = RMS Difference (m) = UTM 17 Eastings (m) x 10 5 Ellipsoidal Elevation (m) Figure 4. North south and east west transects of groundtruth data near Pioneer Park in Deerfield Beach. Project:

8 Figure 5. DEM of area near Pioneer Park. Transect was on NE 2 nd Ave. in Deerfield Beach. Coordinates are in UTM 17 meters, and ellipsoidal elevation in meters. The white line represents the ground profile extracted. Project:

9 East to West Groundtruth Data at LANCON Groundtruth Profile Groundtruth Points LIDAR Profile Mean Difference (m) = 0.13 Standard Deviation (m) = 0.1 RMS Difference (m) = UTM 17 Eastings (m) x 10 5 North to South Groundtruth Data at LANCON Groundtruth Profile Groundtruth Points LIDAR Profile Mean Difference (m) = 0.16 Standard Deviation (m) = RMS Difference (m) = UTM 17 Northings (m) x 10 6 Ellipsoidal Elevation (m) East to West Groundtruth Data at LINCON Groundtruth Profile Groundtruth Points LIDAR Profile Mean Difference (m) = Standard Deviation (m) = RMS Difference (m) = UTM 17 Eastings (m) x North to South Groundtruth Data at LINCON Groundtruth Profile Groundtruth Points LIDAR Profile Mean Difference (m) = Standard Deviation (m) = RMS Difference (m) = UTM 17 Northings (m) x 10 6 Ellipsoidal Elevation (m) Ellipsoidal Elevation (m) Ellipsoidal Elevation (m) Figure 6. North south and east west transects of groundtruth data at the Lantana and Congress intersection (top two graphs), and the Linton and Congress intersection in Palm Beach County (bottom two graphs). Project:

10 Ellipsoidal Elevation (m) Ellipsoidal Elevation (m) East to West Groundtruth Data at PPMIL 21.8 Groundtruth Profile 22 Groundtruth Points LIDAR Profile 22.2 Mean Difference (m) = Standard Deviation (m) = RMS Difference (m) = UTM 17 Eastings (m) x Groundtruth Profile Groundtruth Points LIDAR Profile Mean Difference (m) = Standard Deviation (m) = RMS Difference (m) = North to South Groundtruth Data at PPMIL UTM 17 Northings (m) x 10 6 Figure 7. North south and east west transects of groundtruth data at the Palmetto Park and Military Trail intersection in Palm Beach County. Summary and Conclusions This interim report presents the initial findings of the LIDAR study for Broward County initiated in Summer The summary of these finding is as follows: Data acquisition for the subject areas outlined in the contract agreement were completed successfully Review of initial data sets did not identify any foreseeable problems with further analysis and revealed data of excellent quality At this time the project is still on schedule Future Activities Future activities for this project include the following: Completion of Processing Division of tiles Terrain filtering Project:

11 Construction of DEMs Preliminary Data The attached digital file includes a 2 meter preliminary DEM and preliminary data for an area located near Pioneer Park in Deerfield Beach. Please refer to the filelist.txt for descriptions of data sets. Project:

12 Appendices Appendix A: Flight, System, and Derived Laser Parameters* Date Julian Strip Start Stop Heading Flight Scan PDOP Swath Nominal Footprint Date Name Time Time Height Angle Width Sampling Size (1/2 FOV) Resolution Meters Trans- Long- UTC UTC Degrees Meters Degrees Meters verse itudinal Meters 7/13/ A1 7:13:50 7:19: /13/ A2 7:25:40 7:31: /13/ A3 7:36:29 7:50: /13/ A4 7:52:30 7:52:43 NR NR /13/ A5 7:56:48 8:09: /13/ A6 8:14:07 8:28: /13/ A7 8:32:03 8:45: /13/ A8 8:50:17 9:04: /13/ A9 9:08:04 9:20: /13/ A10 9:24:08 9:37: /13/ A11 9:39:58 9:52: /13/ B1 9:59:38 10:13: /13/ B2 10:15:46 10:28: /13/ B3 10:32:15 10:46: /13/ B4 10:48:39 11:00: /13/ B5 11:04:13 11:17: /13/ B6 11:22:31 11:33: /13/ B7 11:36:30 11:45: /13/ B8 11:49:24 11:56: /13/ B9 12:00:28 12:01: /14/ C1 3:31:03 3:49: /14/ C2 3:52:32 4:02: /14/ C3 4:04:59 4:09: /14/ C4 4:12:30 4:30: /14/ C5 4:32:43 4:38: /14/ C6 4:44:51 4:50: /14/ C7 4:56:15 5:07: /14/ C8 5:07:34 5:07: NR /14/ C9 5:09:02 5:14: /14/ C10 5:16:05 5:23: /14/ C11 5:24:41 5:33: /14/ C12 5:42:51 5:58: /14/ C13 6:00:53 6:18: /14/ D1 6:37:21 6:55: /14/ D2 6:57:39 7:15: /14/ D3 7:21:15 7:39: Project:

13 Date Julian Strip Start Stop Heading Flight Scan PDOP Swath Nominal Footprint Date Name Time Time Height Angle Width Sampling Size (1/2 FOV) Resolution Meters Trans- Long- UTC UTC Degrees Meters Degrees Meters verse itudinal Meters 7/14/ D4 7:45:37 8:05: /14/ D5 8:10:12 8:27: /15/ E1 12:09:09 12:15: /15/ E2 12:19:23 12:24: /15/ E3 12:28:52 12:29: /15/ E4 12:34:01 12:40: /15/ E5 12:41:47 12:47: /15/ E6 12:51:27 12:57: /15/ E7 13:00:20 13:06: /15/ E8 13:09:05 13:15: /15/ E9 13:18:05 13:23: /16/ F1 3:42:13 3:55: /16/ F2 3:58:26 4:16: /16/ F3 4:22:17 4:27: /16/ F4 4:31:32 4:38: /16/ F5 4:41:38 4:47: /16/ F6 4:51:47 4:58: /16/ F7 5:01:29 5:07: /16/ F8 5:12:32 5:19: /16/ F9 5:21:34 5:27: /16/ F10 5:31:55 5:38: /16/ F11 5:41:21 5:47: /16/ F12 5:51:36 6:04: /16/ G1 6:08:13 6:13: /16/ G2 6:17:57 6:24: /16/ G3 6:26:43 6:32: /16/ G4 6:36:50 6:42: /16/ G5 6:46:24 6:51: /16/ G6 6:56:18 7:02: /16/ G7 7:08:23 7:14: /16/ G8 7:17:43 7:23: /16/ G9 7:27:16 7:33: /16/ G10 7:36:44 7:42: /16/ G11 7:46:55 7:52: /16/ G12 7:56:40 8:02: /16/ G13 8:05:53 8:11: /16/ G14 8:17:24 8:23: /16/ G15 8:26:42 8:32: /16/ G16 8:37:27 8:43: /16/ G17 8:46:31 8:52: /17/ H1 4:23:43 4:29: Project:

14 Date Julian Strip Start Stop Heading Flight Scan PDOP Swath Nominal Footprint Date Name Time Time Height Angle Width Sampling Size (1/2 FOV) Resolution Meters Trans- Long- UTC UTC Degrees Meters Degrees Meters verse itudinal Meters 7/17/ H2 4:34:57 4:41: /17/ H3 4:44:58 4:49: /17/ H4 5:05:58 5:09: /17/ H5 5:12:57 5:15: /17/ H6 5:19:31 5:23: /17/ H7 5:28:20 5:31: /17/ H8 5:35:10 5:38: /17/ H9 5:45:29 5:49: /17/ H10 5:53:46 5:59: /17/ H11 6:05:21 6:11: /17/ H12 6:15:04 6:19: /17/ H13 6:27:53 6:30: /17/ H14 6:34:51 6:35: /17/ H15 6:35:45 6:38: /17/ H16 6:41:04 6:43: /17/ H17 6:49:15 6:52: /17/ H18 6:57:24 6:59: /6/ I1 4:18:19 4:20: /6/ I2 4:25:36 4:35: /6/ J1 5:10:14 5:11: /6/ J2 5:27:18 5:33: /6/ J3 5:37:18 5:43: /6/ J4 5:47:20 5:54: /6/ J5 5:58:01 6:04: /6/ J6 6:10:22 6:16: /6/ J7 6:20:56 6:26: /6/ J8 6:30:47 6:38: /6/ J9 6:41:51 6:47: /6/ J10 6:50:41 6:57: /6/ J11 7:00:56 7:06: /6/ J12 7:10:46 7:17: /6/ K1 7:23:56 7:29: /6/ K2 7:34:06 7:40: /6/ K3 7:45:38 7:51: /6/ K4 7:57:02 8:03: /6/ K5 8:07:49 8:13: /6/ K6 8:19:08 8:25: /6/ K7 8:29:40 8:35: /6/ K8 8:39:55 8:43: /6/ K9 8:45:50 8:47: /6/ K10 8:57:54 8:59: Project:

15 Date Julian Strip Start Stop Heading Flight Scan PDOP Swath Nominal Footprint Date Name Time Time Height Angle Width Sampling Size (1/2 FOV) Resolution Meters Trans- Long- UTC UTC Degrees Meters Degrees Meters verse itudinal Meters 8/7/ L1 3:45:46 4:02: /7/ L2 4:10:49 4:27: /7/ L3 4:33:37 4:42: /7/ L4 4:45:10 4:47: /7/ L5 4:51:40 4:53: /7/ L6 4:57:13 4:59: /7/ L7 5:08:27 5:12: /7/ M1 5:13:23 5:15: /7/ M2 5:30:39 5:32: /7/ M3 5:37:44 5:39: /7/ M4 5:45:15 5:47: /7/ M5 5:51:22 5:53: /7/ M6 6:04:26 6:07: *constant parameters not seen on chart include: ground speed 58 m/s; scan rate 21 Hz; and laser pulse rate 10,000 Hz Project:

16 Appendix B: Ground Station Parameters Site Latitude Longitude Ellip. Ht X Y Z RON N W m m m m N W m m m m N W m m m m N W m m m m N W m m m m Project: