Importance of GPS and RS
GPS and remote sensing imagery are primary GIS data sources, and are very important GIS data sources.
GPS data creates points (positions), polylines, or polygons for GIS
Remote sensing imagery are used as major basis map in GIS
Information digitized or classified from imagery are important GIS layers and datasets
Globe Positioning System (GPS)
http://maic.jmu.edu/sic/glossary.htm#Projection
GPS is a Satellite Navigation System
GPS is funded and controlled by the U. S. Department of Defense (DOD). While there are many thousands of civil users of GPS world-wide, the system was designed for and is operated by the U. S. military.
GPS provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time.
At least 4 satellites are used to estimate 4 quantities: position in 3-D (X, Y, Z) and GPSing time (T)
20,000 km
Space Segment The nominal GPS Operational
Constellation consists of 24 satellites that orbit the earth. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. The orbit altitude is such that the satellites repeat the same track and configuration over any point approximately each 24 hours (4 minutes earlier each day). There are six orbital planes, with nominally four SVs (Satellite Vehicles) in each, equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane. This constellation provides the user with between five and eight SVs visible from any point on the earth.
Control Segment
The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado. These monitor stations measure signals from the SVs which are incorporated into orbital models for each satellites. The models compute precise orbital data (ephemeris) and SV clock corrections for each satellite. The Master Control station uploads ephemeris and clock data to the SVs. The SVs then send subsets of the orbital ephemeris data to GPS receivers over radio signals.
User Segment The GPS User
Segment consists of the GPS receivers and the user community. GPS receivers convert SV signals into position, velocity, and time estimates. GPS receivers are used for navigation, positioning, time dissemination, and other research.
Coordinate system and height
GPS use the WGS 84 as datum Various coordinate systems are available for
chosen GPS height (h) refers to WGS84 ellipsoid surface,
so it is a little difference from the real topographic height (H), which refers to the geoid surface, the approximate Mean Sea Level. Some newer GPS units now provide the H by using the equation H=h-N (N from a globally defined geoid, or Geoid99)
H: topographic height or orthometric heighth: ellipsoid heightN: geoid height
H = h - N
http://www.esri.com/news/arcuser/0703/geoid1of3.html
GPS positioning services specified in the Federal Radionavigation Plan
PPS (precise positioning service) for US and Allied military, US government and civil users. Accuracy:
- 22 m Horizontal accuracy- 27.7 m vertical accuracy- 200 nanosecond time (UTC) accuracy
SPS (standard positioning service) for civil users worldwide without charge or restrictions:
- 100 m Horizontal accuracy- 156 m vertical accuracy- 340 nanosecond time (UTC) accuracy
DGPS (differential GPS techniques) correct bias errors at one location with measured bias errors at a known position. A reference receiver, or base station, computes corrections for each satellite signal.
- Differential Code GPS (navigation): 1-10 m accuracy- Differential Carrier GPS (survey):1 mm to 1 cm accuracy
DGPS
The idea behind differential GPS: We have one receiver measure the timing errors and then provide correction information to the other receivers that are roving around. That way virtually all errors can be eliminated from the system
Because if two receivers are fairly close to each other, say within a few hundred kilometers, the signals that reach both of them will have traveled through virtually the same slice of atmosphere, and so will have virtually the same errors
http://www.trimble.com/gps/dgps-how.shtml
real time transmission DGPS or post-processing DGPS reference stations established by The United States Coast Guard and other
international agencies often transmit error correction information on the radio beacons that are already in place for radio direction finding (usually in the 300kHz range). Anyone in the area can receive these corrections and radically improve the accuracy of their GPS measurements. Many new GPS receivers are being designed to accept corrections, and some are even equipped with built-in radio receivers.
http://www.trimble.com/gps/dgps-where.shtml if you don't need precise positioning immediately (real time). Your recorded
data can be merged with corrections recorded at a reference receiver (through internet) for a later clean-up.
http://www.nps.gov/gis/gps/gps4gis/postprocess.html http://www.fs.fed.us/database/gps/cbsalpha.htm
Remote Sensing Basics
Using electromagnetic spectrum to image the land, ocean, and atmosphere.
When you listen to the radio, or cook dinner in a microwave oven, you are using electromagnetic waves. When you take a photo, you are actually doing remote sensing
http://imagers.gsfc.nasa.gov/ems/waves3.html
Types of remote sensing Passive: source of
energy is either the Sun or Earth/atmosphere Sun
- wavelengths: 0.4-5 µm
Earth or its atmosphere- wavelengths: 3 µm -30 cm
Active: source of energy is part of the remote sensor system Radar
- wavelengths: mm-m Lidar
- wavelengths: UV, Visible, and near infrared
Camera takes photo as example, no flash and flash
A. the Sun: energy sourceA. the Sun: energy sourceC. targetC. targetD. sensor: receiving and/or energy sourceD. sensor: receiving and/or energy source
E. transmission, reception, and pre-processingE. transmission, reception, and pre-processingF. processing, interpretation and analysisF. processing, interpretation and analysis G. analysis and applicationG. analysis and application
Passive Remote Sensing Passive Remote Sensing Active Remote SensingActive Remote Sensing
Four types of resolution
Spatial resolution
Spectral resolution
Radiometric resolution
Temporal resolution
Spatial resolution and coverage
Spatial resolution Instantaneous field-of-view
(IFOV) Pixel: smallest unit of an
image Pixel size
Spatial coverage Field of view (FOV), or Area of coverage, such as
MODIS: 2300km or global coverage, weather radar (NEXRAD): a circle with 230 km as radius
30 meter, spatial resolutionNorthwest San Antonio
1 meter, spatial resolutionUTSA campus,
red polygon is the Science Building
Spectral resolution ( ) and coverage (min to max)
Spectral resolution describes the ability of a sensor to define fine wavelength intervals
The finer the spectral resolution, the narrower the wavelength range for a particular channel or band
Radiometric resolution and coverage
Sensor’s sensitivity to the magnitude of the electromagnetic energy,
Sensor’s ability to discriminate very slight differences in (reflected or emitted) energy,
The finer the radiometric resolution of a sensor, the more sensitive it is to detecting small differences in energy
Temporal resolution and coverage
Temporal resolution is the revisit period, and is the length of time for a satellite to complete one entire orbit cycle, i.e. start and back to the exact same area at the same viewing angle. For example, Landsat needs 16 days, MODIS needs one day, NEXRAD needs 6 minutes for rain mode and 10 minutes for clear sky mode.
Temporal coverage is the time period of sensor from starting to ending. For example, MODIS/Terra: 2/24/2000 through present Landsat 5: 1/3/1984 through present ICESat: 2/20/2003 to 10/11/2009
Remote Sensing Raster (Matrix) Data FormatRemote Sensing Raster (Matrix) Data Format Remote Sensing Raster (Matrix) Data FormatRemote Sensing Raster (Matrix) Data Format
0
127
255
Brightness value range
(typically 8 bit)Associated gray-scale
10 15 17 20
15 16 18 21
17 18
20
22
18
20
22 24
1
2
3
4
1 5432Columns ( j)
Bands (k )
1
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4
X axis Picture element (pixel) at location Line 4, Column 4, in Band 1 has a Brightness Value of 24, i.e., BV4,4,1 = 24 .
black
gray
white21
23
22
25
Lines or rows (i)
0
127
255
Brightness value range
(typically 8 bit)Associated gray-scale
10 15 17 20
15 16 18 21
17 18
20
22
18
20
22 24
1
2
3
4
1 5432Columns ( j)
Bands (k )
1
2
3
4
X axis Picture element (pixel) at location Line 4, Column 4, in Band 1 has a Brightness Value of 24, i.e., BV4,4,1 = 24 .
black
gray
white21
23
22
25
Lines or rows (i)
Jensen, 2000Jensen, 2000Jensen, 2000Jensen, 2000
Y ax
is
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