Geospatial Technology and Remote Sensing

Geospatial Technology

Definition of Geospatial Technology

  • Geospatial Technology includes various tools and techniques for the collection, analysis, and visualization of geographic data. This encompasses:

    • Geographic Information Systems (GIS)

    • Global Positioning Systems (GPS)

    • Remote Sensing

Geographic Information System (GIS)

  • A Geographic Information System (GIS) is defined as:

    • A computerized system designed for the storage, retrieval, visualization, and analysis of geographically referenced data.

Remote Sensing

  • Remote Sensing describes the:

    • Process of collecting information related to electromagnetic energy reflected or emitted by a target on the ground.

    • Can be conducted via:

    • Aircraft

    • Spacecraft

  • The devices used to collect this data are often located a considerable distance from the target.

Important Concepts from Lectures on Earth Representation

Datums

  • Datum is defined as:

    • A reference surface of the Earth used for plotting locations on the actual surface.

Earth Shapes

  • Earth Shapes can be characterized by:

    • Ellipsoid/Spheroid: The Earth is modeled as an ellipsoid, larger at its center than at its poles.

    • Geoid: Represents the Earth's surface at mean sea level, aiming to account for irregularities.

    • Geodesy: The science of measuring the Earth's shape to develop models and reference surfaces.

Map Projections

  • Map Projections convert 3D geographical data into a 2D format.

  • Geographic Coordinate System (GCS): A global framework using latitude and longitude to locate positions.

  • Universal Transverse Mercator (UTM):

    • Divided into 60 zones, each spanning 6 degrees of longitude.

    • UTM coordinates are defined as:

    • Easting (x) and Northing (y) coordinates.

    • A grid system divides the world into zones, creating a correspondence between real-world locations and their 2D representations.

    • Most used projection system 

       Cylindrical 

      Conical 

      Azimuthal 

    • Vector model- discrete objects (ex; trees, buildings) physical data (spatially) (Descrete) 

    • Points, line polygon (area) 

    • Point- pair x and y coordinates 

    • Raster data- pixel/cells 

    • Continuous data: temperature, elevation, rainfall 

    • Cell without value is considered null cell 

    • One feature at a time 

Latitude and Longitude

  • Latitude: Imaginary lines, north and south of the equator, ranging from 0 to 90 degrees.

  • Longitude: Imaginary lines running east to west of the prime meridian, spanning 0 to 180 degrees.

Global Positioning System (GPS)

  • GPS is developed by the Department of Defense and operates through:

    • NAVSTAR GPS Satellite Systems, which includes:

    • Space segment

    • Control segment

    • User segment

  • Global Navigation Satellite System (GNSS):

    • First satellite was launched in 1978; the 24th in 1993, marking the initial full operational capability for usage.

  • The equations governing distance are:

    • Distance=Speed×Time(t1−t2)Distance=Speed\times Time\left(t1-t2\right)

    • Where Speed of light is defined as distance/time\text{distance/time}

    • Rearranging provides:

    • Time=DistanceSpeedTime = \frac{Distance}{Speed}


Remote Sensing Details

Remote Sensing Technology

  • Remote sensing technology involves collecting electromagnetic energy reflected or emitted from ground targets using onboard devices.

    • Collects satellite imagery and digital images of Earth using sensors located on orbiting platforms.

Electromagnetic Energy

  • Defined as:

    • A form of energy emitted from objects in electrical and magnetic waves capable of traveling through space.

Types of Remote Sensing Sensors

  1. Active Sensors:

    • Require internal power to operate, do not need sunlight to collect data.

  2. Passive Sensors:

    • Depend on sunlight for data collection; often powered by batteries.

Advantages of Remote Sensing

  • Allows for simultaneous data collection at the same time of day repeatedly.

  • Facilitates large area coverage and monitoring of changes over time.

  • Enables characterization of natural features and physical objects on the ground.

Satellite Sensor Capabilities

  • Defined by four characteristics:

    1. Spectral Resolution: The ability to define the wavelength intervals of electromagnetic energy detected.

    2. Radiometric Resolution: The sensitivity of the sensor to detect slight differences in energy reflected or emitted from the earth.

    3. Spatial Resolution: The smallest details that can be resolved by the sensor, often expressed in meters (e.g., 10 m, 30 m).

    4. Temporal Resolution: The frequency at which data is collected for a specific region.

Notable Space Agencies in the USA

  • NASA: National Aeronautics and Space Administration

  • NOAA: National Oceanic and Atmospheric Administration

  • USGS: United States Geological Survey

Coordinate Conversion Example

  • Converting degrees, minutes, and seconds to decimal degrees:

    • Example: Convert 75 degrees, 35 minutes, and 30 seconds (750 352 302):

    • 75+3560+303600=75+0.583+0.008=75.591675 + \frac{35}{60} + \frac{30}{3600} = 75 + 0.583 + 0.008 = 75.5916

    • Rounded to three decimal places: 75.592 in decimal degrees.

  • Converting decimal degrees to degrees, minutes, and seconds:

    • Example: Convert 75.592 decimal degrees:

    • Degrees: Take the whole number part: 750

    • Minutes: Multiply the remaining decimal part by 60: 0.592×60=35.520.592 \times 60 = 35.52

      • The whole number part is 352.

    • Seconds: Multiply the remaining decimal part of the minutes by 60: 0.52×60=31.20.52 \times 60 = 31.2

      • Round this to the nearest second: 312.

    • Thus, 75.592 decimal degrees is approximately 750 352 312.

Distances/Area Measurement using Google Earth

Major Map Elements

  1. Scalebar: Graphical representation of equivalent distances shown on a map.

  2. North Arrow: Graphical device that orients the map's direction.

  3. Legend: A key that explains various colors and symbols displayed on the map.

    • A well-constructed legend is essential for understanding the symbology of the map.

Types of Maps

  • Reference Map: Displays a variety of information highlighting different features of the landscape.

  • Thematic Map: Focuses on a specific theme, example: demographic data representation.

Digitizing Features in Google Earth

  • Digitization allows for mapping features such as:

    1. Point (e.g., tree, pole)

    2. Line (e.g., road, transmission line, river)

    3. Polygon

  • File types associated with Google Earth include:

    • KML/KMZ:

    • KML stands for Keyhole Markup Language, a file format for representing geographic data.

    • KMZ is a compressed version of KML.

  • ArcMap Data Types:

    • Feature data: .shp

    • Raster data: .grd, .img, .tiff, etc.