1. Ashutosh Bhardwaj and Vikas Thapa
Evaluation of vertical accuracy of ICESat Spaceborne Lidar Data (V34) over Dehradun District Using Open source tools and DGPS data
Ashutosh Bhardwaj and Vikas Thapa
IIRS, Dehradun

2. of the stellar reference system. Source: Zwally et al. (2002).
Outline
Introduction
Objective
Study area
Data & software
Methodology
Analysis and Results
Conclusion
Fig. 1.1 GLAS instrument overview a) Views of GLAS showing the 3 laser boxes (yellow) on the optical
bench, 1-m diameter telescope with shroud, heat pipe (red), and side radiators,
Fig.1 b) The GLAS star tracker (pink), electronics boxes, and the small telescope (grey)
of the stellar reference system. Source: Zwally et al. (2002).

3. Introduction Benefits: Reduced cost Diversity and stability
Open source tools performs a very specific task.
source code is openly published for modification.
Available at no charge under a license defined by the OS initiative.
Programmer improves the source code and shares with general public
User can add or modify existing software as per the need.
Benefits:
Reduced cost
Diversity and stability
simplified collaboration
Flexibility and freedom
Support and accountability
Scalable division of labor

4. ICESat( Ice, Cloud and Land Elevation Satellite)
Laser Altimetry Mission
Launched Jan 12, 2003
Jan 15, 2003 Earth pointing
Operational till 2010
The primary purpose
ice elevation changes.
Secondarey objectives:
measure cloud heights and the vertical structure of clouds and aerosols height profile in the atmosphere
to map the topography of land surfaces (Land Elevation); and to measure roughness, reflectivity, vegetation heights, snow-cover, and
sea-ice surface characteristics.
Geoscience Laser Altimeter System (GLAS) is the sole instrument on board the ICESat which consists of both lidar and altimetry subsystems (18 campaigns).
Mission data is distributed and archived by the National Snow and Ice Data Center (NSIDC)
the GLAS measurements, distributed in 15 science data products, have interdisciplinary applications to land topography, hydrology, and other domains.

5. Inclination: 94 Near circular LEO Orbit. Altitude: 600 km.
Present Study uses freely available GLAS Visualizer (NGAT) tool for evaluation of land elevation derived through ICESat product.
Inclination: 94 Near circular LEO Orbit.
Altitude: 600 km.
Reference System: Geocentric.
Orbital period: 96.6 minutes.
POD
IDL virtual machine executes .sav files without an IDL licence. (source:

6. Objective
Analysis and Re-analysis of the ICESat Release 34 data for the retrieval of terrain elevations
Comparative study with SRTM, ASTER & CartoDEM V2 R1 data.
DGPS survey validation for selected points
Terrain characteristics
plain
undulating terrain.
Accuracy assessment using open source data & DGPS data.

7. Study area Location: west part of uttarakhand (Dehradun district).
Multiple ICESat track passing over dehradun
Analyzed ICESat track over dehradun District

8. DATA ICESat GLA14 Cartosat-1 DEM (Launch date: May 5, 2005, 04:45 UTC)
Latest release data V2 R1 is used
Data reference: WGS84 datum
Spatial resolution: 2.5 m panchromatic band (  µm)
Data acquisition gateway: BHUVAN ISRO (d.o.a.= 7/06/2015)
SRTM Shuttle Radar Topography Mission)
Obtains digital elevation model on a near-global scale from 56°N to 60°N.
Data reference: WGS 84 in horizontal, EGM96 Geoid in vertical Direction. (d.o.a.= 05/01/2015)
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
Japanese sensor which is one of five remote sensory devices on board the Terra.
Data reference : WGS84/EGM96 geoid, horizontal resolution is 1’’ (30 meters) and vertical accuracy is ±20 meters. (d.o.a.= 06/01/2015) (source: Reuter, et al IEEE2009.)

9. ICESat Instrument: GLAS(Geoscience Laser Altimeter System)
Reference: TOPEX/POSEIDON ( source: NSIDC)
Diameter of footprint on surface: 70m
Distance between two footprints: 172m in track Direction
Vertical accuracy: ±14 cm (source: (Schutz, Zwally et al. 2005))
Data acquisition gateway:
(d.o.a.= 7/06/2015)

10. Fig: CartoDEM Raster layer DEM for Dehradun
Cartosat-1 v2 r1 Data
Fig: CartoDEM Raster layer DEM for Dehradun

11. SRTM and ASTER DATA Fig. SRTM90 DEM Raster Layer
Fig. ASTER DEM Raster Layer

12. Release-34 Altimetry
Release 34 contains fixes for several data issues that were determined to exist in the GLAS Release 33 Altimetry data products:
Correction to the ICESat Data Product Surface Elevation due to an Error in the Range Determination from Transmit-Pulse Reference-Point Selection.
Troposphere Correction are improved.
The GLAS product high resolution DEM was determined to have issues in the Southern Latitude when the source was SRTM data. It was reported to have wrong values that showed as banding.
The order of preference for which values are used when the SRTM and CDED overlap was changed. Starting with this release the SRTM is always used in the overlap region.
Some parameters on GLA14 were invalid when i_elev was valid.
GLA12, 13, 14 and 15 atmosphere character confidence flag was always zero.
Occasional mismatch of GLA09 atmosphere characteristic flag value and the value reported on GLA06 and 14.

13. Open source software used
NGAT(altimetry elevation extractor tool) & GLAS visualizer.
Runs on IDL virtual machine
The IDL Virtual Machine (IDL VM) is a runtime version of IDL that can execute IDL '.sav' files without an IDL license
(source:
NGAT extracts elevation from GLA14 binary file.
Extracts: Date,time,Latitude,Longitude& geoid undulation.

14. Methodology
Fig : Methodology Flowchart

15. Reciprocal flattening
Datum
ICESat (GLAS)
WGS 84
Equatorial radius
Polar radius
Reciprocal flattening
Eccentricity
ellipsoid used by ICESat/GLAS is about 70 cm smaller than the WGS-84 ellipsoid.

16. Datum Ellipsoid conversion: Topex/Poseidon to WGS84
Ellipsoid used by ICESat/GLAS is about 70 cm smaller than the WGS 84 ellipsoid (NSIDC FAQ’s)
GLA14 elevation: HWGS84 = h –N - .70
(source: Xioping et al,2012)
h= Topex/Poseidon ellipsoid, N= geoid undulation

17. Results and analysis Total no. of footprints analyzed: 418
Classification: hilly(285), forest(60),agriculture(65),
urban(8)
Table 1.1Statistics for highly steep terrain
parameters
GLAS-CartoDEM
GLAS-SRTM
GLAS-ASTER
footprints
285
Mean(m)
8.20
44.57
55.92
Std. dev(m)
18.50
13.36
17.32
Max(m)
60.37
76.65
106.50
Min(m)
-42.60
18.65
26.72
RMSE(m)
20.20
46.53
58.53
skewness
1.56
1.12
kurtosis
4.57
1.36

18. Table 1.2Statistics for forest area
parameters
GLAS-CartoDEM
GLAS-SRTM
GLAS-ASTER
footprints 60
Mean(m)
9.67
46.35
50.77
Std. dev(m)
6.73
4.50
6.60
Max(m)
60.37
76.65
106.50
Min(m)
-13.76
35.72
27.96
RMSE(m)
11.93
46.56
51.19
skewness
1.09
0.98
0.99
kurtosis
1.45
1.01
Table 1.3Statistics for agriculture area
parameters
GLAS-CartoDEM
GLAS-SRTM
GLAS-ASTER
footprints 65
Mean(m)
1.60
42.43
40.72
Std. dev(m)
5.59
3.39
5.33
Max(m)
60.37
76.65
106.50
min(m)
-23.79
36.71
RMSE(m)
5.50
42.56
41.06
skewness
-1.36
0.97
0.99
kurtosis
7.00
1.02

19. Table 1.4Statistics for urban area
parameters
GLAS-CartoDEM
GLAS-SRTM
GLAS-ASTER
footprints 8
Mean(m)
4.68
44.30
41.68
Std. dev(m)
1.67
2.86
4.53
Max(m)
7.43
50.43
49.43
Min(m)
2.02
41.08
37.34
RMSE(m)
4.93
44.39
41.90
skewness
0.77
0.78
0.79
kurtosis
0.82
0.70
0.72
Table 1.5Comparison of ICESat & DGPS elevation
S.no.
ICESat elevation
V34(m)
DGPS elevation
(m)
DGPS-ICESat
Terrain
type 1.
521.98
517.30
-4.64
hill 2.
510.13
509.27
-0.86 3.
534.29
525.80
-8.48
forest 4.
592.12
591.45
-0.66
Agri. 5.
593.46
592.52
-0.94

20. Geolocation of footprints
Fig: geolocated shot of ICESat footprint on agriculture terrain.(courtesy: google earth)
Fig: geolocated shot of ICESat footprint on highly steep terrain. (Courtesy: google earth)

21. Fig. 1.1 ICESat-CartoDEMV2R1 (hilly area)
Fig. 1.2 ICESat-CartoDEMV2R1 (agri. area)
Fig. 1.3 ICESat-CartoDEMV2R1 (forest area)
Fig. 1.4 ICESat-CartoDEMV2R1 (urban area)

22. Fig. 1.5 ICESat-SRTM (forest area)
Fig. 1.6 ICESat-SRTM(urban area)
Fig. 1.7 ICESat-SRTM(hilly area)
Fig. 1.8 ICESat-SRTM(agriculture area)

23. Fig. 1.9 ICESat-ASTER (agriculture area)
Fig ICESat-ASTER (hilly area)
Fig. 4.1 ICESat-ASTER (urban area)
Fig. 4.1 ICESat-ASTER (Forest area))

24. R² values & correlation
s.no.
DATASET
R² value 1.
ICESat - CartoDEM (hill having steep slope)
0.9986 2.
ICESat - CartoDEM(agri.)
0.9863 3.
ICESat - CartoDEM(forest)
0.9954 4.
ICESat - CartoDEM(urban)
0.9096 5.
ICESat – SRTM (hill having steep slope)
0.9993 6.
ICESat - SRTM(agri.)
0.9942 7.
ICESat - SRTM(Forest)
0.9979 8.
ICESat - SRTM(urban)
0.7791 9.
ICESat – ASTER (hill having steep slope)
0.9989
10.
ICESat - ASTER(agri.)
0.9876
11.
ICESat - ASTER(forest)
0.9956
12.
ICESat - ASTER(urban)
0.8852
Observation shows that SRTM90(Forest) has the best correlation with ICESat height among SRTM90, CartoDEM v2, ASTER & the lowest correlation was achieved for SRTM90(urban) area.

25. Conclusion
Present study shows utility of open source data and free NGAT tool in the analysis.
The RMSE found to be quite high in the highly rough terrain as compared to the low undulating area.
On the flat terrain, the elevation values given by ICESat LiDAR are nearly matching with DGPS values, whereas for the rough terrain depending on the steepness the variations are high because of large footprint.
RMSE for the CartoDEM was found to be 20.20m, 11.93m, 5.50m, and 4.93m for hilly, forest, agriculture and urban terrain respectively.

26. Conclusion
For highly rough terrain skewness values are found to be quite high as compared with low elevation area.
Regression plots analysis shows the correlation between forest area and highly slopping terrain.
DGPS survey shows that slopping highly undulating terrain having less accuracy as compared to the low elevation area.
From the analysis CartoDEM data accuracy was found to be quite high as compare to other datasets.
Observation shows that SRTM90(Forest) has the best correlation with ICESat height among SRTM90, CartoDEM v2, ASTER & the lowest correlation was achieved for SRTM90(urban) area.

27. Future
Thank y u