GPS and Remote Sensing

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) 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.

55°

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 height h: ellipsoid height N: geoid height H = h - N

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 m vertical accuracy nanosecond time (UTC) accuracy SPS (standard positioning service) for civil users worldwide without charge or restrictions: m Horizontal accuracy m vertical accuracy 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.

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. 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

Remote sensing platforms

Types of remote sensing Passive: source of energy is either the Sun or Earth/atmosphere Sun - wavelengths: 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 source C. target D. sensor: receiving and/or energy source E. transmission, reception, and pre-processing F. processing, interpretation and analysis G. analysis and application G. analysis and application Passive Remote Sensing Active Remote Sensing

NASA Research Spacecraft

Busy TrafficData acquisition

The greatest canyon on Mars: Valles Marineris

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 resolution Northwest San Antonio 1 meter, spatial resolution UTSA campus, red polygon is the Science Building

Spatial Resolution Jensen, 2000

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

Comparing a 2-bit image with an 8-bit image

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 Format Remote Sensing Raster (Matrix) Data Format Jensen, 2000 Y axis

Image processing and modeling Image processing and modeling Soil moisture Surface temperture and albedo RainfallETSnow and Ice Water quality Vegetation cover Land use The size of a cell we call image resolution, depending on… Such as 1 m, 30 m, 1 km, or 4 km