Today s Agenda. GPS Imagery (optical and radar)

Transcription

1 Today s Agenda GPS Imagery (optical and radar) Topography For more info on Remote Sensing, there is a class: Introduction to the Physics of Remote Sensing (EE/Ge 157 abc)

2 GPS Our use of GPS: Location of surveys O(m) Topographic corrections for gravity surveys O(cm) Could make a high res DEM (not needed) We will use both hand held GPS and RTK GPS RTK = real time kinematic, a form of differential GPS

3 28 GPS satellites Designated by PRN (1-33) or SVN/GPS number (currenlty, 1-59) GPS constellation Each GPS satellite is in a 26,000 km orbit Each satellite broadcasts unique ranging codes and ephemeris information for the entire constellation Each satellite has its own response to non-gravitational forces such as solar pressure and commanded maneuvers Position in the orbit is known to about 2 cm (eventually) Civilian and other uses require only 1-10 meter orbit knowledge Scientific users demand much more

4 What is GPS? GPS is a timing system Clocks Ranging based on time of flight of signal from transmitter to receiver Plus Media delays Instrument delays Physical models

5 GPS Signal Structure L-band carriers with ranging codes L1 CA ~300 m P-code (pseudorange) ~ 30 m Y-code (an encryption on top of P-code) Anti-Spoofing (AS) L2 P-code Y-code (an encryption on top of P-code) Anti-Spoofing (AS) L2C Block IIRM (2005) BlockIIRF, GPS-III (2008) L5 GPS-III CA

6 Low Precision Users Simple receivers Track L1 Minimum of 4 satellites tracked Use ranging code and broadcast ephemeris to triangulate Precision limited by Orbit error Clock error Selective Availability (SA) Ranging errors Propagation delays Typical civilian user Hiker Automobiles Etc.

7 High Precision User More complex receivers Track phase of L1, L2, and ranging codes Sophisticated tracking loops Cross correlated observations for minimizing Y-code Track all satellites visible (8-12) Collect carrier phase, ranging codes, and broadcast ephemeris Better antennas Multi-path is an issue Post processing Determine position and other parameters using observations and precise ephemeris

8 APPLICATION: 3-D Crustal Motion Tectonic motion Ocean tides Solid earth tides Subsidence Glacial isostatic adjustment Monument stability GLOBAL POSITIONING SYSTEM GPS Satellite / Orbits / Clocks Propagation Ionosphere Troposphere (wet & dry) GPS Receiver Clocks Multipath Antenna phase center variation Geometric dilution of precision (GDOP) 24 Total Satellites Minimum 4 necessary to correct receiver clock errors

9 CONTINUOUS (PERMANENT) GPS Give daily/sub-daily positions Provide significantly more precise data: No errors in setting up equipment and reoccupying sites Stable monuments More positions to constrain secular rates Can observe transient signals such as due to earthquake

10 Early Mobile GPS Technology JPL s SERIES Codeless Receiver c (Satellite Emission Radio Interferometric Earth Surveying)

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12 Remote Sensing

13 Character of imagery is based on the reflectance and backscatter characteristics of the surface, f(l) Different materials have different spectral behavior (rocks of different kinds, water, vegetation ) Both material type + physical state of material are important Holy grail: automatic geological classification using limited training. Keep searching Note that the spectral information available to us limited by the fact that we typically image through the atmosphere

14 Atmospheric absorption Spectra of common vegetation + Spectra of common rocks/minerals

15 Critical questions to ask when using imagery 1. Spatial resolution (pixel size) 2. Image extent (General rule: target is always on the boundary) 3. Wavelength 4. $$$$ Common systems Platform Pixel (m) Extent (km) Cost ($) Aster 15/30 60 FREE!!!!!! Landsat 4,5,7 15/ $400+* Landsat 8 5/ FREE!!!!!! Sentinel-2ab 10/ FREE!!!!!! (5 day repeat, 13 bands) SPOT** 5/10 60 O(1000) Ikonos*** 1/4 10 O(1000) Planes/Helicopter O(10cm) 10**** Quickbird, Worldview, * Perhaps now free ** French *** Military **** Camera + height above ground

16 Landsat: Only 7 spectral bands, not very useful for discerning material types But because of large image spatial extent and reasonable resolution, good for overview

17 ASTER (14 bands) Instrument VNIR SWIR TIR Bands Spatial resolution 15m 30m 90m Swath width 60km 60km 60km Cross track pointing ±318km(± 24 ) ±116km(± 8.6 ) ±116km(± 8.6 )) Quantization (bits) Note: Band 3 has nadir and backward telescopes for stereo pairs from a single orbit.

18 Example: Aster band combination Saline Valley Assign different l bands or combination of bands to RGB to form color image Thermal infrared bands 13, 12 and 10 as RGB Variations in: quartz content appear as more or less red; carbonate rocks are green mafic volcanic rocks are purple

19 Sentinel 2 ab Band number Central wavelength (nm) Band width (nm) Lref (Wm 2 sr 1 μm 1 ) Lref b

20 Hyperspectral Imagery Multiple bands (images) each at different wavelengths e.g. AVIRIS bands Large data volumes!

21 At radar wavelengths, the atmosphere is transparent Frequencies and Wavelength of the IEEE Radar Band designation Band Frequency (GHz) Wavelength (cm) L S C X Ku K Ka

22 SAR/InSAR Platforms Aircraft: Shown here: AIRSAR Measures topography, ocean currents Satellites: Repeat pass Fly over once, repeat days-years later Images Measures deformation and topography Space shuttle: Shuttle Radar Topography Mission (SRTM) From: H. Zebker Both from: JPL

23 Radar is active imaging Natural image coordinates are in units of time: along track (azimuth direction) & lineof-sight (LOS) (range direction) foreshortening layover shadows Imaging radar is side looking (why?) Achieve resolution by clever combination of consecutive radar images: Synthetic Aperture Radar (SAR)

24 Mapping timeàspace

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26 Topography (DEM, DTM, DTED, topo, height, ) Methods Land surveys (now GPS) Radar altimeter Air or space borne laser (LIDAR) - point or swath mapping altimeter Stereo imagery (air photos, now satellite) Radar interferometry a.k.a. InSAR (plane, shuttle, satellite) Practical availability U.S.: m/px (USGS, SRTM) on the net m (Airborne InSAR, optical, LIDAR) - e.g., TOPSAR Foreign: 90 m/px (SRTM 60S-60N), m/px by begging (classified) 900 m/px open access Make your own (InSAR, optical) 1-20 m/px

27 Practical Concerns with Imagery and DEMs 1. Postage stamp continuity 2. Reference mapping information Origin Datum (ellipsoid - WGS84, NAD27) Projections q UTM - eastings and northings (m) q Geographic - longitude and latitude (deg) 3. File format # px in x and y coordinates How to store multiple bands (BIL, BIP) Precision (bytes/band/pixel) - always in binary 4. Software (raster + vector) ESRI - ArcGIS ERDAS - Imagine Matlab/IDL GIS permits easy use of data bases and geographical logic Python: matplotlib+basemap+gdal+. 5. Imaging combinations Shaded relief (intensity) + color (something else) Use Google Earth for simple tasks

28 What is shaded relief? Directional gradient mapped to grey scale

29 Cajon Pass I-15 Fault Crossing

30 Getting LIDAR data Get an account Click on data select with map Choose B4 and/or Dragons Back (what s the difference?) Select point cloud and have it make the DEM. You probably want shaded relief KMZ as well as geotiff/img for ARC. May need to download in overlapping tiles because of file size limits and odd shape of target area Submit and wait for

31 GIS Homework (due in 2 weeks!) Construct basemaps of the Carrizo Plain region. Your map should be annotated with any geologically interesting features (faults, major geomorphic structures, place names, roads etc.) and include scale bars and geographic reference (ticks or something) as well as legends for any colors or symbols that you use. All annotations should be useful (choose units appropriately) and legible. Your basemap(s) can use any useful combination of DEMs and imagery. Feel free to experiment! Make it clear what imagery you are using and how you chose your colors. You will use these maps in 111b to orient yourself in the field, to document where we went, and even possibly to do some geology Feel free to use the GIS lab on the 3 rd floor of South Mudd as much as you need for this assignment. Lisa Christensen, the Lab manager, will provide an overview on the use of ARC GIS if you have not used it before. Extract and plot a 1-km-long topographic profile perpendicular to the SAF near our proposed field area. Make sure the profile is nicely annotated. Show the location of the profile on your map. Measure offset features along the fault. Is there any obvious pattern? Indicate which features you are measuring on one of your maps.