GPS, Photogrammetry and Remote Sensing

Transcription

1 GPS, Photogrammetry and Remote Sensing Lecture 11 November 30, 2006

2 Why GPS, orthophotos, and imagery in GIS? GPS, orthophotos 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

3 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 (L1 at MHZ for civilian GPS and L2 at MHZ for precision mode) 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). 3 satellites for X, Y, T 20,000 km

4 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.

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6 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.

7 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.

8 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 of the WGS 84 datum, so it is a little difference from the real topographic height (H). the difference is the geoid height (N). Geoid surface is 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) All current Garmin, Magellan, Lowrance models report height above the geoid H: topographic height or orthometric height h: ellipsoid height N: geoid height H = h - N

9 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

10 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.

11 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 Electromagnetic Basics Using electromagnetic spectrum to image the land, ocean, and atmosphere.

12 MGS TES 6 50 µm Source: Stan Aronoff, 2005

13 What is Photogrammetry Photogrammetry is the art and science of making accurate measurements by means of aerial photography: Analog photogrammetry (using films: hard-copy photos) Digital photogrammetry (digital images) Aerial photographs were the first form of remote sensing imagery. Differences between photogrammetry and Remote Sensing are that photographs are: Black and white (1 band) or color (blue, green, red, and IR) Wavelength range of µm Use cameras One type of remote sensing imagery

14 Types of vantage points to acquire photographs Vertical vantage points Low-oblique vantage points High-oblique vantage points

15 Vertical Aerial Photography Camera film plane Vertical Aerial Photograph Over Level Terrain Altitude above-groundlevel (AGL) field of view Gooseneck s s of of the the San San Juan Juan River River in in Utah Utah Optical axis Principal point (PP) 90 Jensen, Jensen, Most are vertical aerial photography

16 Low-oblique oblique Aerial Photography Low-Oblique Aerial Photograph Over Flat Terrain field of view 90 Optical axis Horizon is not shown in photograph Jensen, Jensen, Low-oblique oblique photograph of of a a bridge bridge on on the the Congaree River River near near Columbia, SC. SC.

17 High-oblique Aerial Photography High-Oblique Aerial Photograph Over Flat Terrain High-oblique photograph of of the the grand grand Coulee Coulee Dam Dam in in Washington in in field of view Optical axis Horizon is shown in the photograph 90 Jensen, Jensen,

18 Types of photographs Black and white photographs Panchromatic (minus-blue filter used to eliminate UV and blue wavelengths) IR (IR-sensitive film and IR only filter used to acquire photographs at µm ) UV (at µm, low contrast and poor spatial resolution due to serious atmospheric scattering) Color photographs Normal color (Haze filter used to absorb UV and create true color µm, or blue, green, red) IR color (Yellow filter used to eliminate blue and create IR color (or false-color infrared) of µm, or green, red, IR) 4 bands (blue, green, red, and IR)

19 Normal color False-color infrared

20 Orthorectification

21 Remote sensing platforms

22 Satellite Based Sun-synchronous polar orbits Most earth imaging satellites is polar-orbiting, meaning that they circle the planet in a roughly north-south ellipse while the earth revolves beneath them. Therefore, unless the satellite has some sort of "pointing" capability, there are only certain times when a particular place on the ground will be imaged global coverage, fixed crossing, repeat sampling typical altitude 500-1,500 km example: MODIS, Landsat Non-Sun-synchronous orbits tropics and mid-latitudes coverage, varying sampling typical altitude 200-2,000 km example: TRMM Geostationary orbits regional coverage, continuous sampling over low-middle latitudes, altitude 35,000 km

23 Passive Remote Sensing Active Remote Sensing A. the Sun: energy source E. transmission, reception, and pre-processing processing C. target F. processing, interpretation and analysis D. sensor: receiving and/or energy source G. analysis and application

24 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

25 Four types of resolution Spatial resolution Spectral resolution Radiometric resolution Temporal resolution

26 30 meter, spatial resolution Northwest San Antonio 1 meter, spatial resolution UTSA campus, red polygon is the Science Building

27 Spatial Resolution Jensen, Jensen,

28 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 Soil moisture Surface temperture and albedo ET Rainfall Snow and Ice Water quality Vegetation cover Land use