LAB 1 METHODS FOR LOCATING YOUR FIELD DATA IN GEOGRAPHIC SPACE · YOUR FIELD DATA IN GEOGRAPHIC...

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Transcript of LAB 1 METHODS FOR LOCATING YOUR FIELD DATA IN GEOGRAPHIC SPACE · YOUR FIELD DATA IN GEOGRAPHIC...

  • LAB 1

    METHODS FOR LOCATING

    YOUR FIELD DATA IN

    GEOGRAPHIC SPACE

    Geog 315 / ENSP 428

  • Lab 1 Schedule

    Introduction to bio-physical field data collection (8:00-8:20am)

    Locating your data on the earth: NAVSTAR Global Positioning System (8:20-9:20am)

    -- 15-min Break --

    Quiz (9:35-10:00am)

    Measuring distance and azimuth(10:00-10:30am)

    --15-min Break

    Planning the field campaign (10:45am-11:10am)

    Introduction to Trimble Juno GPS units and Impulse laser rangefinder(11:10am-11:40pm)

  • Lab Objectives

    Understand the spatial dimension of field data, and the costs and benefits of collecting it

    Understand how the Global Positions System (GPS) works, its advantages, and its limitations

    Understand how distance between points can be surveyed with laser rangefinders, and know when this technology is appropriate to use

    Learn how to effectively plan for a field campaign to increase sampling efficiency and spatial and attribute data accuracy

    Exposure to GPS units and laser rangefinders used in Lab 2

  • Collecting bio-physical field data

  • La Selva Biological Field Station

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    1000 0 1000 Meters

    Soils / SuelosOld alluvium / Aluvion viejoRecent alluvium / Aluvion recienteResidual

    Stream-associated / Suelo de quebradasSwamp / Pantano

    # Species present / Presencia del especies

    N

    Dipteryx panamensis

  • Elephant herd home range

    http://www.save-the-elephants.org

  • Spatial information

    Most spatial information of interest is geographic

    can be placed on the earth

    Spatial information links a place with a property of that

    place The temperature is 40 C at

    Latitude: 38 N, Longitude: 122 W

    Could also be at a specific time The temperature is 40 C at Latitude: 38 N, Longitude: 122 W at

    02/13/2009, 8 am

    Properties are variables that we measure sensed

    with our body or instruments

    Can be quantitative or qualitative

    The potential number of geographic places and their

    properties is vast

  • Some bio-physical variables of interest

    Biological plants, animals, fungi, etc.

    Composition presence/absence, abundance of species or groups, communities

    Vegetation structure biomass, height, diameter, percent cover, leaf area index

    Physical environment variables

    Moisture, temperature, light

    Geological composition

    Chemistry of soil, water or air (e.g., nutrients, pollution)

    Geomorphology shape of the land, including slope, aspect, elevation

    Disturbance and threats

    Natural: fire, wind-throw, pest attack, species invasion

    Anthropogenic: deforestation, poaching, grazing

  • Sampling geographic information

    Type

    Single points

    Transects along a line

    Plots

    Rapid assessment visit

    Scale

    Space boundary area; geographic area or length of samples; distribution of samples

    Time -- return interval. Once every year? Need to come back to location? Need to leave a monument?

    Considerations

    Preliminary assessment or long-term monitoring

    Time

    Money

    Access

  • Global Navigation Satellite Systems

    (GNSS)

    Locating your data on the earth

  • Global Navigation Satellite Systems (GNSS)

    Most common approach to surveying locations is using Global Navigation Satellite Systems (GNSS)

    It uses range measurements based on radio signals from satellites

    Systems developed by USA, Russia, European community and China

  • Developed, owned and maintained by the U.S. Department of Defense (US$400 million per year to maintain)

    Accurately determines horizontal location, elevation and speed

    Almost anywhere on earth

    day or night

    any weather

    Free for public use!

    NAVSTAR

    Global Positioning System (GPS)

  • GPS segments

  • GPS satellite segment

    32

    http://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.html

    http://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.htmlhttp://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.htmlhttp://science.nasa.gov/Realtime/jtrack/3d/JTrack3D.html

  • GPS user segment

  • GPS General Information

    GPS satellites broadcast three different types of data using radio waves

    1. Almanac data

    - system health and rough orbits of all GPS satellites; tells receiver which satellites to listen for

    2. Ephemeris data for the broadcasting satellite;

    - allows a GPS receiver to accurately calculate the position of the broadcasting satellite

    - satellite health, clock corrections, etc.

    3. Coded signals

    - Coarse Acquisition code, or C/A, and the Precise code, or P-code (C/A code used mainly in civilian applications)

  • Range = speed of light x travel time

    Range = c(t1 t0)

    (c =299,792,458 meters per second)

    t0

    t1

    A single satellite

    range measurement

  • GPS code receiver

    Assume that satellite and receiver are generating the same pseudo-random code at exactly the same time

  • Measurements to multiple satellites determines position

  • Sources of Error

    Several factors can result in erroneous location

    determination with GNSS (or GPS)

    Source Range Error (m)

    Satellite clock error 1

    Satellite position error 1

    Atmospheric & Ionospheric effects 4

    Receiver error 1.5

    Total ~7.5

    Positional uncertainty (1)

  • Positional uncertainty (2)

    Leads to positional

    uncertainty

  • Ionosphere

    http://www.aiub.unibe.ch/ionospherehttp://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/ion.html

    Electrified region within the upper atmosphere Can reflect, deflect and scatter radio waves increase range

  • Source:http://www.garmin.com/aboutGPS/

    Multipath signal error

  • Positional Dilution of Precision (PDOP)

  • Obstructions to satellite signals

    Telescoping pole

  • Adjusting PDOP thresholds

    Typically want PDOP < 6

  • Types of receivers (1)

    Many types of receivers on the market vary in price, features and performance

    Most now are multi-channel (12) can track up to 12 satellites

    Ability to average points

    Ability to change projection and datum

    Display screen for features and maps

    Memory to hold features and properties (attributes)

    Ability to download data

    Battery life

    Differential corrections (more on this coming)

    Antennas that reduce error

  • Types of receivers (2)

    Recreational receivers - $200 to $1000

    Mapping grade - $1000 - $10,000

    Set PDOP, satellite elevation and signal-to-noise filters

    Target satellites

    Point averaging

    Differential corrections

    Data dictionary and data download

    High-end survey grade

    Better antennas

    Can achieve centimeter accuracy

  • Differential correction

  • For each satellite, the roving (receiver) range is corrected by the observed range error at base station

    Differential correction

  • Two common

    types of

    differential

    GPS

    Best performance

    if base station

    within 180 miles,

    300 km

  • CORS - Continuously Operating Reference Stations

    National Geodetic Survey (NGS), an office of NOAA's National Ocean Service, coordinates a network of Continuously Operating Reference Stations (CORS) base stations

    Each CORS site provides carrier phase and code range measurements for differential correction

    GNSS - GPS and GLONASS supported

    CORS data are available at their original sampling rate for 30 days, after that at reduced sampling rate

    http://www.ngs.noaa.gov/CORS/

    http://www.ngs.noaa.gov/CORS/

  • CORS

    http://www.ngs.noaa.gov/CORS/GoogleMap/

    http://www.ngs.noaa.gov/CORS/GoogleMap/http://www.ngs.noaa.gov/CORS/GoogleMap/http://www.ngs.noaa.gov/CORS/GoogleMap/http://www.ngs.noaa.gov/CORS/GoogleMap/http://www.ngs.noaa.gov/CORS/GoogleMap/http://www.ngs.noaa.gov/CORS/GoogleMap/

  • Measuring distance and azimuth angles

  • Distance and azimuth measurements

    Offset points: We can locate a fixed point with a GPS (GNSS) receiver and then calculate the horizontal position of other points relative to the GPS point with distance and azimuth (bearing) angle measurements

    The GPS point in this context is called a control point

    Azimuth: the clockwise angle from north, e.g. 45o

    (northeast), 180o (south) i.e., bearing

    The accuracy of this technique depends on accuracy of instruments used to measure

    Geographic position (e.g., GPS)

    Angle (e.g., analog or digital compass)

    Distance (e.g., tape measure, laser rangefinder)

  • Compass

    Measures azimuth angles

    0 to 360

  • Magnetic declination

    Earth has a geographic north and south pole axis

    upon which the planet spins

    Earth is like a big magnet; liquid iron-nickel core

    creates magnetic field

    Compass needles point in the direction of the

    magnetic field lines North on a compass, or 0 is

    magnetic north, not geographic north

    Magnetic declination - angle between the compass

    pointing direction and geographic north, or true

    north

  • http://www.ngdc.noaa.gov/geomagmodels/struts/calcDeclination

  • Distance

    Tape measures

  • Laser rangefinder

    Maximum

    Range575 m

    Accuracy 3 - 5 cm typical

    Inclinometer

    Range 90 degrees

    Inclinometer

    Accuracy 0.1 deg. typical

  • Horizontal distance

    Want horizontal distance, or planimetric distance --

    may need to slope correct

    A

    B

    hd = horizontal distance

    = inclination angle

    Cos () = hd/sd (adjacent/ hypotenuse)

    hd = sd * Cos ()

    can be measured with a inclinometer

    or laser rangefinder inclinometer

  • Vertical height

    Some applications require measurement of height

    Same concepts apply

    hd = horizontal distanceA

    B

    1

    Tan() = vh/hd (opposite/adjacent)

    vh1 = hd * Tan(1)

    vh1 = vertical height

    vh2= vertical height2

    C

    vhtotal = vh1 + vh2

  • Measuring tree height, La Selva, Costa Rica

  • Using the Laser Tech Impulse

  • Mapping a point

    Forest

    GPS control point &laser rangefinder

    x

    y

    Sin () = x/hd (opposite/ hypotenuse)x = Sin () * hd

    Cos () = y/hd (adjacent/ hypotenuse)y= Cos () * hd

    Trunkx = GPSx + x

    Trunky = GPSy + y

    0 N

  • Field Plot

    Mapping a polygon (1)

    Collecting corner x,y positions with a GPS receiver

    GPS positional error

  • Field Plot

    Mapping a polygon (2)

    Collecting corner x,y positions with a GPS receiver

    and differential corrections (DGPS)

    DGPS positional error

  • Field Plot

    Mapping a polygon (3)

    Collecting corner x,y positions with DGPS and laser

    rangefinder

    Control pointDGPS positional error

    Laser rangefinderpositional error

    Closure?

  • Planning the field campaign

  • Project fundamentals

    Define research question and goals

    Consider a spatial perspective in questions

    Ask how spatial data and sampling scheme help

    answer this

    Familiarize yourself with study area

    Logistics of getting there

    What type of obstacles canopy cover, mountains

    Permissions for access, other cultural issues

  • Project fundamentals (cont)

    Resolution and accuracy needs

    Spatial and temporal scale

    Type of equipment: recreational or mapping-grade

    GPS?

    Tape measure or laser rangefinder?

    Data collection methodology

    Points, lines or areas

    Coordinate system and projection

    How data collected? Who?

    How data stored data dictionary, on a paper form

  • Long-term field plots

  • Field data

    form

  • Data dictionary

    A data dictionary is a "shopping list" of the features and their attributes that you want to map in the field

    You create the data dictionary with the GPS vendors software (e.g., Pathfinder Office) prior to going into the field

    You then upload the data dictionary to your GPS receiver

    Once in the field, the data dictionary prompts you for information for each spatial feature (e.g., point, polygon) measured

    Provides a standard format for data entry

    Saves time!

    Helps prevent input errors!

  • Mission planning software

    GPS (GNSS) vendors generally provide mission planning software with receiver

    Free software is from Trimble

    Almanac information on satellites is available from Trimble, http://www.trimble.com/gpsdataresources.shtml

    http://www.trimble.com/planningsoftware.shtml

    http://www.trimble.com/gpsdataresources.shtmlhttp://www.trimble.com/gpsdataresources.shtmlhttp://www.trimble.com/planningsoftware.shtmlhttp://www.trimble.com/gpsdataresources.shtml

  • Data dictionary

  • GPS satellites - 02/26/2010

  • Sky plot

    Rohnert Park, CA 02/26/2010

  • Number of satellites Santa Rosa, CA

    Rohnert Park, CA 02/26/2010

  • PDOP Santa Rosa, CA

    Rohnert Park, CA 02/26/2010

  • Sonoma State Campus June 2007