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)

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

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 heighth: 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, 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

http://www.trimble.com/gps/dgps-how.shtml

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.

http://www.trimble.com/gps/dgps-where.shtml 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.nps.gov/gis/gps/gps4gis/postprocess.html http://www.fs.fed.us/database/gps/cbsalpha.htm

http://www.trimble.com/gps/dgps-how.shtml

http://www.geoplane.com/gpsneeds.html

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

http://imagers.gsfc.nasa.gov/ems/waves3.html

Remote sensing Remote sensing platforms platforms

Types of remote sensing Passive: source of

energy is either the Sun or Earth/atmosphere Sun

- wavelengths: 0.4-5 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 sourceA. the Sun: energy sourceC. targetC. targetD. sensor: receiving and/or energy sourceD. sensor: receiving and/or energy source

E. transmission, reception, and pre-processingE. transmission, reception, and pre-processingF. processing, interpretation and analysisF. processing, interpretation and analysis G. analysis and applicationG. analysis and application

Passive Remote Sensing Passive Remote Sensing Active Remote SensingActive Remote Sensing

NASA Research

Spacecraft

Busy Traffic Data 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 resolutionNorthwest San Antonio

1 meter, spatial resolutionUTSA campus,

red polygon is the Science Building

Spatial Spatial ResolutionResolution

Spatial Spatial ResolutionResolution

Jensen, 2000Jensen, 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 FormatRemote Sensing Raster (Matrix) Data Format Remote Sensing Raster (Matrix) Data FormatRemote Sensing Raster (Matrix) Data Format

0

127

255

Brightness value range

(typically 8 bit)Associated gray-scale

10 15 17 20

15 16 18 21

17 18

20

22

18

20

22 24

1

2

3

4

1 5432Columns ( j)

Bands (k )

1

2

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4

X axis Picture element (pixel) at location Line 4, Column 4, in Band 1 has a Brightness Value of 24, i.e., BV4,4,1 = 24 .

black

gray

white21

23

22

25

Lines or rows (i)

0

127

255

Brightness value range

(typically 8 bit)Associated gray-scale

10 15 17 20

15 16 18 21

17 18

20

22

18

20

22 24

1

2

3

4

1 5432Columns ( j)

Bands (k )

1

2

3

4

X axis Picture element (pixel) at location Line 4, Column 4, in Band 1 has a Brightness Value of 24, i.e., BV4,4,1 = 24 .

black

gray

white21

23

22

25

Lines or rows (i)

Jensen, 2000Jensen, 2000Jensen, 2000Jensen, 2000

Y ax

is

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