GPS, Photogrammetry and Remote Sensing

Lecture 11

November 30, 2006

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 GISInformation digitized or classified from imagery are GIS layers

Globe Positioning System (GPS)

GPS is a Satellite Navigation SystemGPS 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

http://maic.jmu.edu/sic/glossary.htm#Projection

20,000 km

Space SegmentThe nominal GPS Operational Constellation consists of 24satellites 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 SegmentThe 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 heightGPS use the WGS 84 as datumVarious coordinate systems are available for chosenGPS 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). Geoidsurface 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 ororthometric height

h: 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, USgovernment 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 DGPSreference 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 TES6 – 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)

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 0.3-1.0 µmUse camerasOne type of remote sensing imagery

Types of vantage points to acquire photographs

Vertical vantage pointsLow-oblique vantage points High-oblique vantage points

Vertical Aerial PhotographyVertical Aerial PhotographyVertical Aerial Photography

Altitude above-ground- level (AGL)

Vertical Aerial Photograph Over

Level Terrain

90°

Principal point (PP)

Optical axis

Camera film plane

field of view

Goosenecks of the

San Juan River

in Utah

GooseneckGoosenecks of the s of the

San Juan San Juan River River

in Utahin Utah

Jensen, 2000Jensen, 2000Jensen, 2000

Most are vertical aerial photography

Low-oblique Aerial PhotographyLowLow--oblique Aerial Photographyoblique Aerial Photography

Low-Oblique Aerial Photograph Over

Flat Terrain

Horizon is not shown in photograph

Optical axis

90°

field of view

Low-oblique photograph of a bridge on the Congaree River near Columbia, SC.LowLow--oblique photograph of a bridge on oblique photograph of a bridge on the Congaree River near Columbia, SC.the Congaree River near Columbia, SC.

Jensen, 2000Jensen, 2000Jensen, 2000

High-oblique Aerial PhotographyHighHigh--oblique Aerial Photographyoblique Aerial Photography

High-Oblique Aerial Photograph Over

Flat Terrain

90°

Horizon is shown in the photographOptical

axis

field of view

High-oblique photograph of the grand Coulee Dam in Washington

in 1940

HighHigh--oblique photograph of the oblique photograph of the grand Coulee Dam in Washington grand Coulee Dam in Washington

in 1940in 1940

Jensen, 2000Jensen, 2000Jensen, 2000

Types of photographsBlack 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 0.7- 1.0 µm )UV (at 0.3-0.4 µm, low contrast and poor spatial resolution due to serious atmospheric scattering)

Color photographsNormal 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 Remote sensing platforms

Satellite Based

Sun-synchronous polar orbitsMost 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 imagedglobal coverage, fixed crossing, repeat samplingtypical altitude 500-1,500 kmexample: MODIS, Landsat

Non-Sun-synchronous orbitstropics and mid-latitudes coverage, varying samplingtypical altitude 200-2,000 kmexample: TRMM

Geostationary orbitsregional coverage, continuous samplingover low-middle latitudes, altitude 35,000 kmexample: GOES

Passive Remote Sensing Passive Remote Sensing Active Remote SensingActive Remote Sensing

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 preE. transmission, reception, and pre--processingprocessingF. processing, interpretation and analysisF. processing, interpretation and analysis

G. analysis and applicationG. analysis and application

Types of remote sensingPassive: source of energy is either the Sun or Earth/atmosphere

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

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

Radar- wavelengths: mm-mLidar- wavelengths: UV, Visible, and near infrared

Camera takes photo as example, no flash and flash

Four types of resolution

Spatial resolution

Spectral resolution

Radiometric resolution

Temporal resolution

1 meter, spatial resolutionUTSA campus,

red polygon is the Science Building

30 meter, spatial resolutionNorthwest San Antonio

Spatial Resolution

Spatial Spatial ResolutionResolution

Jensen, 2000Jensen, 2000

Image processing Image processing and modelingand modeling

Image processing and

modeling

Soil moisture

Surfacetempertureand albedo

RainfallET Snowand Ice

Waterquality

Vegetationcover

Landuse

The size of a cell we call image resolution, depending on…Such as 1 m, 30 m, 1 km, or 4 km