GPS, Photogrammetry and Remote Sensing

Lecture 11 November 30, 2006

Why GPS, orthophotos, and imagery in GIS? „

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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

Globe Positioning System (GPS) „ „

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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 1575.42 MHZ for civilian GPS and L2 at 1227.6 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

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

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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 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 http://www.esri.com/news/arcuser/0703/geoid1of3.html

GPS positioning services specified in the Federal Radionavigation Plan „

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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 „

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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

Electromagnetic 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

MGS TES 6 – 50 µm

Source: Stan Aronoff, 2005

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)

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Aerial photographs were the first form of remote sensing imagery.

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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 0.3-1.0 µm Use cameras One type of remote sensing imagery

Types of vantage points to acquire photographs

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Vertical vantage points Low-oblique vantage points High-oblique vantage points

Vertical Vertical Aerial Aerial Photography Photography Vertical Aerial Photograph Over Level Terrain

Camera film plane

Altitude above-groundlevel (AGL)

field of view

Gooseneck Gooseneck ssofofthe the San SanJuan Juan River River ininUtah Utah

Optical axis

Principal point (PP) 90°

Jensen, Jensen,2000 2000

Most are vertical aerial photography

Low -oblique Aerial Low-oblique Aerial Photography Photography Low-Oblique Aerial Photograph Over Flat Terrain

field of view

Optical axis

90°

Jensen, Jensen,2000 2000

Horizon is not shown in photograph

Low -oblique photograph Low-oblique photographof ofaabridge bridgeon on the theCongaree CongareeRiver Rivernear nearColumbia, Columbia,SC. SC.

High -oblique Aerial High-oblique Aerial Photography Photography High-Oblique Aerial Photograph Over Flat Terrain

High -oblique photograph High-oblique photographofofthe the grand grandCoulee CouleeDam DamininWashington Washington inin1940 1940

field of view

Optical axis

Horizon is shown in the photograph

90°

Jensen, Jensen,2000 2000

Types of photographs „

Black and white photographs „

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Panchromatic (minus-blue filter used to eliminate UV and blue wavelengths) IR (IR-sensitive film and IR only filter used to acquire photographs at 0.7- 1.0 µm ) UV (at 0.3-0.4 µm, low contrast and poor spatial resolution due to serious atmospheric scattering)

Color photographs „

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Normal color (Haze filter used to absorb UV and create true color 0.4-0.7 µm, or blue, green, red) IR color (Yellow filter used to eliminate blue and create IR color (or false-color infrared) of 05-1.0 µm, or green, red, IR) 4 bands (blue, green, red, and IR)

Normal color

False-color infrared

Orthorectification

Remote sensing platforms

Satellite Based „

Sun-synchronous polar orbits „

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Non-Sun-synchronous orbits „ „ „

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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

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 example: GOES

Passive Remote Sensing

Active Remote Sensing

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

Types of remote sensing „

Passive: source of energy is either the Sun or Earth/atmosphere „

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Sun - wavelengths: 0.4-5 µm Earth or its atmosphere - wavelengths: 3 µm -30 cm

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Active: source of energy is part of the remote sensor system „

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Radar - wavelengths: mm-m Lidar - wavelengths: UV, Visible, and near infrared

Camera takes photo as example, no flash and flash

Four types of resolution „

Spatial resolution

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Spectral resolution

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Radiometric resolution

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Temporal resolution

30 meter, spatial resolution Northwest San Antonio

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

Spatial Spatial Resolution Resolution

Jensen, Jensen,2000 2000

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