Mc Rmp Srt m Tutorial

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MINISTRY OF MARINE AFFAIRS AND FISHERIES

Directorate General of Coastal and Small Islands

Jl. M.T. Haryono Kav, 52-53, Jakarta Selatan, Indonesia. Fax.(62)(21) 79180456

BLACK & VEATCH (International) Ltd

In association with:

MARINE & COASTAL RESOURCES MANAGEMENT PROJECT

Package B

SPATIAL DATA AND INFORMATION MANAGEMENT PROJECT

ADB Loan No. 1770-INO (SF)

Creating DEM from SRTM – UPDATED Version

Technical Report MCRMP-B-SRTM

DEM created from SRTM for Tanimbar, Indonesia

October 2004

Nusantara Systems International

PT EXSA Internasional



MCRMP - Marine and Coastal Resources Management Project

Component B: Spatial Data and Information Management

Black & Veatch (International) Ltd in association withPT Nusantara Systems International and PT Exsa Internasional

TABLE OF CONTENTS

TABLE OF CONTENTS.............................................................................. ........................................................ 2

SRTM DATA..................................... ............................................................ ........................................................ 2

1. INTRODUCTION................................................................................. ........................................................ 2 2. SRTMFILL.............................................................. ........................................................... ........................... 2

3. 3DEM ................................................... ........................................................... ............................................... 3

4. SURFACE MODELING.................................................. ........................................................... ............... 10

4.1 CREATING A TIN ........................................................... ........................................................... ............... 13 4.2 CREATING A R ASTER DEM ..................................................... ........................................................... ..... 14 4.3 CALCULATING SLOPE .................................................... ........................................................... ............... 15

APPENDIX 1. SRTM QUICK FACTS....................................................... ...................................................... 17

SRTM DATA

1. INTRODUCTION

The Shuttle Radar Topography Mission (SRTM) was a joint project between the National Geospatial-Intelligence Agency (NGA) and the National Aeronautics and Space Administration (NASA). Theobjective of this project was to produce digital topographic data for 80% of the Earth's land surface(all land areas between 60° north and 56° south latitude), with data points located every 1-arc second(approximately 30 meters) on a latitude/longitude grid. The absolute vertical accuracy of the elevationdata was estimated to be 16 meters (at 90% confidence). The SRTM was flown on Space ShuttleEndeavour from 11 – 23 February 2000. The data has two resolutions: 30 m for conterminous USAand 90 m for remaining land masses. A web site has been set up with information on the data and

various products at http://srtm.usgs.gov/. The data is freely available and can be downloaded from theUSGS site ftp://edcsgs9.cr.usgs.gov/pub/data/srtm. The data is downloaded in HGT format in 1degree tiles; this raw data needs preprocessing and converted to geoTIFF or other supported format

before it can be used. Two steps are needed for the preprocessing:

1). Null and bad data needs to be replaced using SRTMFill; and

2). The HGT format tiles need to be mosaiced and written out as geoTiff.

Note that this updated tutorial replaces an earlier version published in July 2004. This version removesthe need for editing and greatly simplifies the procedures for creating a DEM from SRTM. Because itis automated it can be programmed with ArcGIS 9 model builder. A training manual has been writtenthat describes the methods for creating a spatial model with Model Builder.

2. SRTMFILL

The study area can be identified using srtmgrid shapefile in the PSIC geodatabase. The PSIC infobasealso has a link to a zipped file srtmgrid.zip which can be downloaded. Search for SRTM in theinfobase to locate the grid. Write down the tiles that are required and download them from the SRTMftp site if you do not have them. Copy SRTMFill.exe from the CD to this directory. SRTMFill is aDOS program and does not need to be installed. Unzip the HGT files and run SRTMFill. You willhave to wait a few seconds for the request for registration to time out (see below)

SRTMTutorial.doc 2 BL/21-Oct-04 12:45:00 PM

http://srtm.usgs.gov/

ftp://edcsgs9.cr.usgs.gov/pub/data/srtm

ftp://edcsgs9.cr.usgs.gov/pub/data/srtm

http://srtm.usgs.gov/






Ready to run now

Wait for registerwindow to timeout

3. 3DEM

Install program 3DEM off the accompanying CD, run the program and Load Terrain Model (see below)

SRTM Data (hgt)Load Terrain Model

Load ONLY the filled HGT tiles. These can be easily identified by the ‘_fill.hgt’ in the file name.

For this example you should see the terrain shown in the figure below. The tiles selected for this

example are Tanimbar S07E131; S08E130; S08E131; S09E130 and S09E131.







For many applications which require slope or aspect, the DEM cannot be in decimal degrees.However, change projection in 3DEM has a number of limitations if SRTM tiles:

• Span the equator you cannot convert mosaiced SRTM to UTM projection;

• Cross UTM zones;

For this reason it is probably best to write the mosaiced SRTM out as geoTiff in decimal degrees (see below) and use ArcToolBox to reproject the SRTM to UTM or some other projection.

1. File

2. Save GeoTiff DEM

If none of the constraints listed above apply then it is best to change the projection of SRTM to UTM(see below).

Convert to UTM







As before the SRTM is saved as geoTiff (see below). In this example I have called the DEMtanimbarutm.tif.

Save GeoTiff DEM

The limitations are worth repeating:

• TILES CANNOT SPAN THE EQUATOR IF UTM OUTPUT WANTED;

• TILES CANNOT SPAN UTM ZONES IF UTM OUTPUT WANTED; and

• THERE IS A LIMITATION ON THE NUMBER OF TILES THAT CAN BE LOADED (ABOUT9);

The data is now added to ArcMap. If the data is in decimal degrees then it needs to be reprojectedusing ArcTool > Project Raster (see below).

Cell size (SRTMis 90 m)

Projection(UTM52S in thisexample)

Projected Raster output

GeoTiff input

Project Raster

Projections &Transformations

SRTM geotiff indecimal degrees

NOTE! The cell size of SRTM is 90 m1.

1 Ninety meters (90 m) in decimal degrees is 0.0008333 at the equator and for practical purposes can be used as aconversion for all Indonesia.







When this is done you will notice that there are negative values even though SRTMFill was used sinceit only fills null values. You may also note that there are positive values in areas of sea. It is necessaryto replace these negative values with zero and also to replace offshore areas that have positive valueswith zeros.

To remove negative values use Spatial Analyst raster calculator (see below). NOTE: Make sure the

spatial analyst extension is activated. NOTE: If the raster calculator does not work close ArcMap andthen run it again.

DEM

Note negativevalues

Spatial Analyst

Raster Calculator

Use the conditional statement which in this example is:

con([tanimbarutm.tif] < 0, 0, [tanimbarutm.tif])

This is a Visual Basic- like command and is interpreted as if the raster value of tanimbarutm.tif isless than zero then replace the raster value with zero otherwise replace it with the original value.

You will notice now that negative values have been replaced, however, there are still many rasters inthe sea with values greater than zero - these are wrong and must be corrected using a land mask.







elevation > 0 insome areas ofwater

The only sure way to replace these with zero is to use a land mask. Land features digitized fromLandsat 7 ETM + is included on CD; add this to ArcMap. NOTE: Landsat and SRTM are registeredto each other; however, SRTM is 90 m resolution, whereas Landsat multispectral is 30 m. Thisguarantees that the coastline extracted from heads-up-digitizing will closely match the SRTM.

Reproject land shape file included on CD from decimal degrees to UTM. Make sure the UTM zone isthe same as the SRTM. ESRI has a number of map data sets and one of these called UTMZones isvery useful for determining the UTM zone. Alternately use the figure below to determine the UTMzone. Note that Tanimbar is UTM zone 52 South.

Tanimbar

Convert land from vector to raster using Spatial Analyst. However, before this is done we need toknow the raster size. To determine what the raster cell size is open the properties of tanimbarutm.tif .

Note that the raster cell size is 90 m.







Raster cell is 90 m

Moreover we need a value to assign to the raster cells. To do this open the attribute table of tanlnd, adda field called X452 (any nonsense name will do), and use the calculator to assign the value of 1 to allfeatures.

X452

Cell size (90 m)

Features to raster

Thus when the DEM map is multiplied by the raster land mask the sea areas are 0 and the land areaskeep their elevation.







Raster calculation








4. SURFACE MODELING

BAKO 1:50,000 map sheets have 25 m elevation contours. Contouring can be done in either SpatialAnalyst or 3D Analyst.

25 m

25 m

Contour

Use contour interval of 25 m and base contour of 0 m. This will give 25 m contours. Open the attributetable and use Options > Select by attribute to select all contours less than 25 m (see below).

2. Open Attribute Table

1. Select ctour > right button

4. Select byAttribute

3. Options






Contour < 25

Start Editing and delete all contours less than 25 m (i.e. selected contours). Note that the coastline (0m elevation) will be missing. The coastline can be added as the 0 m contour using the GeoprocessingWizard > Merge in ArcMap Tools. However, we must first convert the land polygons to DXF2 andthen convert the line DXF to shapefile (or feature class in personal geodatabase). This is done withArcToolBox > Conversion Tools > Shapefile to DXF (see below).

Editor > Start Editing

Once they are deleted Stop Editing.

There may be some instances where the elevation contours cross the coastline such as areas that havesteep slopes and hills or mountains next to the coast. To create a clean DEM we need to clip thecontours. However a simple clip will result in some intersections that may have two elevations: 0 fromthe coastline and 25, 50 or even higher elevation from the contours. Therefore it is best to buffer thecoastline and use the buffer to clip the elevation contours. Experience has shown that 45 m is anappropriate buffer distance given the spatial resolution of the SRTM (90 m) and the base map which

was derived from heads-up digitizing of Landsat 7 ETM satellite imagery. To create a buffer we mustfirst convert tanlnd from polygon to polyline (see below).

2 ArcGIS Version 8 you must first convert to DXF because it does not have a tool to convert polygon to polyline;in Version 9 we can convert directly from polygon to polyline using ArcToolbox > Features Tools.







Output feature class

tanlnd

Polygon to Line

tanlnd

Next we buffer the coastline at 45 m (see below) using the ArcTool Buffer. Note that the optiondissolve ALL is selected.

ALL

45 m

Polyline

Polyline

Once the buffer has been created we need to clip the elevation contours. To do this we use the ArcToolErase (see below).








Erase

Elevationcontours

Erase features is45 m buffer

45 m Buffer

4.1 Creating a TIN

Elevation contourclipped 45 m fromcoastline

The coastline and the elevation contours can be used to create a TIN. However, the coastline needs anattribute that is 0 which is the elevation at the coast. Open the attribute table of the coastline and add afield called contour type double. Set the default to 0.

Option > Add Field

Calculatevalues and setcontour = 0

Default: 0

Type: Double

Name: Contour






Use 3D Analyst to create a TIN. Add coastline as hard line which forces the TIN to go through thecoast at 0 m and add the contours as either soft line or mass points (see below).

Coastline as hard lines

Elevation contours as mass points

Hard lines at coastline

4.2 Creating a Raster DEM

Once the TIN has been created you need to convert it back to raster using 3D Analyst. During this stepthe cell size can be specified. To have the raster DEM conform to SRTM cell size of 90 m (map unitsare in meters) (see below).







90 m

TIN to Raster

Convert

4.3 Calculating Slope

Use 3D Analyst or Spatial Analyst to calculate slope (see below). NOTE: To properly calculate slopeand aspect, map units need to be in meters. This requires that the raster DEM be in UTM. Use degreesfor output measurement.

Output measurement degreeSlopeSurface Analysis

The MCRMP data dictionary specifies that slope be classified into 5 categories (see table below).

K_SLOPE SLOPE

1 0-2%

2 2-15%

3 15-25%

4 25-40%

5 > 40%

To classify the slope data use Spatial Analyst > Reclassify (below). Save the reclassification scheme.







Convert the raster to vector using Spatial Analyst.

Other surfaces can be computed such as aspect. The same procedures follow as above. If necessaryreclassify and convert to vector feature class. Make sure the reclassification scheme is saved so that acorrect legend can be made.







APPENDIX 1. SRTM QUICK FACTS

MISSION: QUICK FACTS

Shuttle Radar Topography MissionStatistics

Update 3/14/00

Mission Statistics:Launch: February 11, 2000, 12:44 pm ESTLanding: February 22, 2000, 6:22 pm EST at Kennedy Space CenterMission Duration: 11 days, 5 hours, 38 minutesProject Start: August 1996Project End: March 2001Project Life Cycle: 60 months (42 months start to launch; 18 months data processing)

Data StatisticsLand coverage: Targeted land was 80% of Earth landmass (119.56 M km2, 46.16 M mi2)99.968% targeted land mapped at least once (119.51 M km2, 46.14 M mi2)94.59% targeted land mapped at least twice (113.10 M km2, 43.66 M mi2)49.25% targeted land mapped at least 3 times (58.59 M km2, 22.73 M mi2)24.10% targeted land mapped at least 4 times (28.81 M km2, 11.12 M mi2)

Land area missed: 50,000 km2 (all in US)

Data Takes: 765 total399 C-band only1 X-band only365 C and X-band simultaneous674 data takes over land61 Built In Test Equipment (BITE) data takes28 'short' ocean calibration data takes2 'long' ocean calibration data takes

Data Tapes: 330 total high-density tapes used208 tapes with C-band data, plus one double-recorded (pilot) tape122 tapes with X-band data, plus one double-recorded (pilot) tape(C-band tapes each recorded ~ 30 min. of data at 180 Mbits/sec,X-band tapes recorded 60 min. of data at 90 Mbits/sec, and were onaverage 73% utilized)

Data Acquisition: 222.4 hours total duration of mapping phase99.2 hours C-band operation90.6 hours X-band operation8.6 Terabytes C-band data (=14,317 CDs)3.7 Terabytes X-band data (=6101 CDs)12.3 Terabytes total data (=20,418 CDs)(Approx. equal to Library of Congress)

Data Played Back 104 C-band playbacksDuring Flight 49 X-band playbacks

Energy used: 902.8 kWh (911 kWh planned)

Payload Weight: approximately 13,600 kg(approximately 29,000 lbs or 14.5 tons)

Mission Costs:: $133M Mission Development Costs without Launch Delay$8.2M Launch Delay Costs$142M Total Mission Cost







$50M Launch Costs$40M X-SAR Costs

Mission Objective:To use C-band and X-band interferometric synthetic aperture radars (IFSARs)to acquire topographic data over 80% of Earth's land mass (between 60degN and56degS) during an 11-day Shuttle mission. Produce digital topographic map

products which meet Interferometric Terrain Height Data (ITHD)-2 specifications(30 m x 30 m spatial sampling with <=16 m absolute vertical height accuracy,<= 10 m relative vertical height accuracy and <=20 m absolute horizontalcircular accuracy). All accuracies are quoted at the 90% level, consistent with National Map Accuracy Standards.

Mission Firsts:o Fixed baseline single-pass spaceborne interferometric SARo Dual frequency (C-band and X-band) interferometric SARo Largest rigid structure flown in space

Mast Information:

Mast Length 60 m 200 feet Nominal Mast Diameter 1.12 m 44.12 in Nominal Bay Width at Longerons 79.25 cm 31.20 in Nominal Bay Length 69.75 cm 27.46 in Number of Bays 87Canister Diameter (at largest ring) 1.36 m 53.5 inStack Height/Bay 1.59 cm 0.63 inCanister Length 2.92 m 115 inMast Mass 290 kg 640 lbCanister Mass 695 kg 1530 lbMast Material: longeron material is carbon fiber reinforced plastic (CFRP);

Diagonal materials include stainless steel and alpha titanium.Ball joints are made from hardened stainless steel.

Mast Construction: AEC-Able Engineering Company, Inc. (ABLE), Goleta, California

Mission Sponsors: National Imagery and Mapping Agency (NIMA) National Aeronautics and Space Administration (NASA)German Aerospace Center (DLR, Deutsches Zentrum für Luft- und Raumfart)Italian Space Agency (ASI, Agenzia Spaziale Italiana)

Project Management:Jet Propulsion Laboratory

Data Product Applications:o Scientific applications:Geology, geophysics, earthquake research, volcano monitoringHydrologic modeling

Co-registration of remotely acquired image datao Civilian applications:Enhanced Ground Proximity Warning Systems for aircraftCivil engineering, land use planningLine of sight determination for communications (e.g. cell phones)o Military applications:Flight simulatorsLogistical planning, trafficabilityMissile and weapons guidance systemsBattlefield management, tactics







Implementationo Modifying and adding to SIR-C/X-SAR instruments flown successfully as

Space Radar Laboratory Missions (SRL-1, April 1994; SRL-2 October 1994)o Partnership: Major new components provided by industry.

Mission Manifest:

o STS-99 Shuttle Endeavouro SRTM was a single payload missiono Shuttle travelled tail forward at 7.5 km/sec (17,000 mph)o Attitude was rolled 59 deg from the bay-down orientation, placing the mast at 45 deg

from verticalo Nominal altitude: 233 km (approximately126 nautical miles, 145 statute miles) with

orbital adjustment once per dayo 150 data acquisition orbits plus activation, on-orbit checkout and de-activationo 6-member crew to activate payload, deploy and stow mast, align inboard and outboard

antennas, monitor payload flight systems, operate on-board computers & recorders, &handle contingencies

STS-99 Crew

Commander: Kevin KregelPilot: Dom GorieMission Specialists: Janet Kavandi, Janice Voss,Mamoru Mohri (NASDA), Gerhard Thiele (ESA)

Significant Contractors:o AEC-ABLE Engineering, Goleta, CA (deployable mast & canister)o America Technology Consortium, Camarillo, CA, (motors and actuators)o Ball Telecommunication Products Division, Boulder, CO (outboard antenna)o Daimler-Benz Aerospace (Dornier Satellite Systems), Friedrischafen, Germany (X-band radar system)o Composite Optics Inc., San Diego, CA (composite outboard structure)o ENERTEC, France (onboard high rate recorders)o Lockheed Martin, Palo Alto, CA (star tracker)o Mission Space, La Canada, CA (command & telemetry systems)

o JDS Uniphase Corporation, Chalfont, PA (calibration optical link)


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