GPS and Remote Sensing Lecture 20 April 7, 2004
Why GPS and RS in GIS? • 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 • Remote sensing imagery and airphotos are used as major basis map in GIS • Information digitized or classified from imagery are GIS layers
Globe Positioning System (GPS) • 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 http://maic.jmu.edu/sic/glossary.htm#Projection
Space Segment • The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth in 12 hours. 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 ellipsoid surface, so it is a little difference from the real topographic height (H). the difference is the geoid height (N), 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 – Geoid99) H: topographic height or orthometric height h: ellipsoid height N: 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) • 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. • 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.fs.fed.us/database/gps/cbsalpha.htm
Project tasks can often be categorized by required accuracies which will determine equipment cost.
Remote Sensing Basics • Using electromagnetic spectrum to image the land, ocean, and atmosphere. http://imagers.gsfc.nasa.gov/ems/waves3.html 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
Passive Remote Sensing Active Remote Sensing E. transmission, reception, and pre-processing F. processing, interpretation and analysis G. analysis and application A. the Sun: energy source C. target D. sensor: receiving and/or energy source
Major Passive: Multi-Spectral Sensors • LANDSAT MSS/TM/ETM+ (NASA, USA) • SPOT-1, -2, -3 (France) • JERS-1 (optical sensor) (Japan) • MODIS (NASA, USA) • AVHRR (NOAA, USA) • ASTER (NASA, USA, and Japan) • IRS-1A, -1B, -1C, 1D (India) • IKONOS (Space Imaging, USA) Hyper-Spectral Sensor • AVIRIS (NASA, USA) • HyMap (Australia)
Major Active:Radar Sensor • SIR-A, -B, -C (NASA, USA) • RADARSAT (Canada) • JERS-1 (radar sensor) (Japan) • ERS-1 (European) • AIRSAR/TOPSAR (NASA, USA) • NEXRAD (NOAA, USA) • TRMM (NASA, USA) Lidar Sensor • ALTMS (TerraPoint, USA) • FLI-MAP (John Chance, USA) • ALTM (USA) • TopoEye (USA) • ATLAS (USA)
Spectrum Visible Near Infrared Thermal Infrared Bands 8 Resolution (m) 15, 30, 60 NASA Landsat-7 (ETM+) launched 4/15/1999 705 km
Terra satellite launched on 12/18/1999 Spectrum Visible Near Infrared Thermal Infrared Bands 36 Resolution (m) 250, 500, 1000 705 km http://terra.nasa.gov/About/MODIS/modis_swath.html
N. & S. American Eastern Pacific Europe and Africa Jap. Aus. W. Paci C. Asia, India Ocean China, India Ocean Global Geostationary Satellites Earth radius 6,370 km Satellite altitude 35,800 km
Soil moisture Surface temperture and albedo ET Rainfall Snow and Ice Water quality Vegetation cover Land use Image processing and modeling The size of a cell we call image resolution, depending on… Such as 1 m, 30 m, 1 km, or 4 km Image processing and modeling