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Ge111A Remote Sensing and GIS Lecture
Remote Sensing - many different geophysical data sets. We concentrate on the following:
Imagery (optical and radar)Topography
Geographical Information Systems (GIS) a way to organize the imagery as well as point, line, and shapefile data; useful for cataloguing and searching regional data bases
Note:Positions and Positions (GPS @ end of quarter)For more info on RS, there is a class:
Introduction to the Physics of Remote Sensing (EE/Ge 157 abc)
Why use GIS in a field geophysics class?
Understand what is in the field as best you can before you go there: Terrain & topography Geology Roads Access Geomorphic features (faults, mountain ranges, etc)
Add your own data and locations to the map (locations of survey points and/or lines)
Easily produce base maps showing where different surveys were conducted during the class activities
Equations relating wavelength, frequency, and speed:
If the wave travels at the speed of light, c
c=0.3 m/ns = 3x108 m/s.
A wave with a frequency of 1015Hz has a wavelength, , of 3 x 10-7 m, which is 300 nm or 0.3 m in the ultraviolet part of the spectrum.
1) What happens to the wave if it travels in a medium with speed less than the speed of light?
2) Can you find the mistake in the graph on this page?
Measurements conducted from:SatellitesAircraftHandheld sensors
Character of imagery is based on the reflectance and backscattercharacteristics of the surface, f()
Different materials have different spectral behavior (rocks of different kinds, water, vegetation)
Both material type + physical state of material (grain size, weathering) are important
Ways you could correct for atmospheric absorption
Make atmospheric observations simultaneous with the remote sensing (hard to get usually) Use an atmospheric model of absorption based on other dates or locationsMake surface spectrometer measurements for calibration, during the survey or during similar season and time as original surveyDont use bands in the spectral area of max. absorption
Spectra of common rocks/minerals
Spectra of common vegetation +
From Hunt (1977) spectral locations of absorption signals for different minerals and rocks
Sensitive to: energy states of electrons in outer shells of transition metals (visible wavelengths)
Twisting, rotation, vibrations of bonds in compounds (3-14 micron region)
Critical questions to ask when using imagery
1. Spatial resolution (pixel size)2. Image extent (General rule: target is always on the boundary)3. Wavelengths 4. $$$$
Platform Pixel (m) Extent (km) Cost ($)Aster 15/30 60 FreeLandsat 4,5,7 15/30 180 $400+*SPOT** 5/10 60 O(1000)Ikonos*** 1/4 10 O(1000)Planes/Helicopter O(10cm) 10**** ----
* A variety of cheaper combos exist** French*** Military**** Camera + height above ground
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
Instrument VNIR SWIR TIRBands 1-3 4-9 10-14Spatial resolution 15m 30m 90mSwath width 60km 60km 60kmCross track pointing 318km( 24) 116km( 8.6) 116km( 8.6))Quantization (bits) 8 8 12
Note: Band 3 has nadir and backward telescopes for stereo pairs from a single orbit.
ASTER (14 bands)
Example:Aster band combination
Assign different bands or combination of bands to RGB to form color image
Thermal infrared bands 13, 12 and 10 as RGB
quartz content appear as more or less red;
carbonate rocks are green
mafic volcanic rocks are purple
Multiple bands (images) each at different wavelengths
e.g. AVIRIS - 224 bands
Large data volumes!
What is the advantage of hyperspectral images?
Much narrower wavelength bands easier to see smaller features in the absorption spectrum.
At radar wavelengths, the atmosphere is transparent
Frequencies and Wavelength of the IEEE Radar Band designation
Band Frequency (GHz) Wavelength (cm)L 1-2 30-15S 2-4 15-7.5C 4-8 7.5-3.75X 8-12 3.75-2.50Ku 12-18 2.5-1.67K 18-27 1.67-1.11Ka 27-40 1.11-0.075
Both from: JPLFrom: H. Zebker
Satellites: Repeat passFly over once, repeat days-years laterImagesMeasures deformation and topography
Space shuttle:Shuttle Radar Topography Mission (SRTM)
Aircraft: Shown here: AIRSARMeasures topography, ocean currents
Radar is active imaging
Natural image coordinates are in units of time: along track & line-of-sight (LOS) range
Imaging radar is side looking (why?)
Achieve resolution by clever combination of consecutive radar images: Synthetic Aperture Radar (SAR)
Land surveys (now GPS or total station)Radar altimeterAir or space borne laser - point or swath mapping altimeterStereo imagery (air photos, also now satellite)Radar interferometry a.k.a. InSAR (plane, shuttle, satellite)Optical interferometry a.k.a. LIDAR
U.S.: 10-30 m/px (USGS, SRTM) on the net0.5-15 m (Airborne InSAR, optical, laser swath) - e.g., TOPSAR
Foreign: 90 m/px (SRTM 60S-60N), 30-60 m/px by begging (classified)900 m/px open access
Make your own (InSAR, optical) 10-20 m/px
Topography (DEM, DTM, DTED, topo, height,)
Practical Concerns with Imagery and DEMs1. Continuity of adjacent images2. Reference mapping information
Origin Georeferencing how many tie points are needed? Datum (WGS84, NAD27, NAD83) Projections
UTM - eastings and northings (m)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 (ENVI software) GIS permits easy use of data bases and geographical logic
5. Imaging combinations Shaded relief (intensity) + color (something else) Use Google Earth for simple tasks
The next few images are from Jane Dmochowskis PhD thesis (Caltech SeismoLab, 2005)
Isla San Luis is an active volcanic island in the Gulf of California (Mexico)
The imagery is Modis-Aster Simulator (MASTER) airborne data, with about a 4 m pixel size. It was collected with a very low-flying small airplane.
The MASTER sensor has 50 spectral bands from visible to thermal infrared (TIR).
LIDAR images of San Andreas fault from P4 project (high resolution topography) can see through the trees
LIDAR light detection and ranging works at optical frequencies
Cajon Pass I-15 Fault Crossing
Another example of LIDAR data for topography along the San Andreas fault
Ge111a GIS project
Topo map (USGS) SPOT image ASTER bands 1-3 Landsat-Thematic Mapper bands 1-3 DEM made from TOPSAR Geographic features (roads, drainages)
Homework due Thurs April 19th
1. Construct a basemap(s) of the greater Queen Valley region. Annotate your map with any geologically interesting features (faults, major alluvial fans, place names etc.) and include scale bars and geographic reference (ticks or something) as well as legends for any colors or symbols that you use.
Print out your map to turn in, but save the file so you can use it later on in the class.
2. Make a perspective image of the Queen Valley fault using Google Earth or similar product (based on aerial photographs and an unknown DEM). Turn this in with your HW.
3. Write a paragraph comparing the strengths and weaknesses of the different data types you have available in the GIS project (DEM, shaded relief DEM, Aster, SPOT). Discuss the different types of natural and man made features that are detectable. Dont forget the railroad grade and the aqueduct.
The GIS Lab is available to you all the time. For workstation use, students doing classwork have priority over those doing research. There will be two sessions on Tuesday in the GIS lab: one at 9 and one at 10.
Tuesday 4/10 GIS lab sessions309 North Mudd
Why use GIS in a field geophysics class?Cajon Pass I-15 Fault CrossingGe111a GIS projectTuesday 4/10 GIS lab sessions309 North Mudd