LAB 1 METHODS FOR LOCATING YOUR FIELD DATA IN GEOGRAPHIC SPACE. Geog 315 / ENSP 428

Transcription

1 LAB 1 METHODS FOR LOCATING YOUR FIELD DATA IN GEOGRAPHIC SPACE Geog 315 / ENSP 428

2 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) 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)

3 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

4 Collecting bio-physical field data

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6 La Selva Biological Field Station

7 Dipteryx panamensis # Species present / Presencia del especies Soils / Suelos Old alluvium / Aluvion viejo Recent alluvium / Aluvion reciente Residual Stream-associated / Suelo de quebradas Swamp / Pantano # ## # # ## # # ## # ## ## ## # # ## ## # ## ## ## # ## ## ## # ## # # ## ## ## # # # # # ## # # ## # ## ## ## ## # # ## # ## # # ## # ## # # # # # # ## # # # # ## # # ## # ## ## # ## ## # ## ## ## # ## # # # # ## ## # ## ## ## # # # # ## # # ## ## # ## ## ## # # # # # ## ## ## # # # # # ## # # # # # # # ## # # ## # # # # # # # ## # # # # # ## ## # ## # N Meters

8 Elephant herd home range

9 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

10 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

11 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

12 Locating your data on the earth Global Navigation Satellite Systems (GNSS)

13 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

14 NAVSTAR Global Positioning System ( GPS ) 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!

15 GPS segments

16 GPS satellite segment 32

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18 GPS user segment

19 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)

20 A single satellite range measurement t 0 t 1 Range = speed of light x travel time Range = c(t 1 t 0 ) (c =299,792,458 meters per second)

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

22 Measurements to multiple satellites determines position

23 Positional uncertainty (1) 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

24 Positional uncertainty (2) Leads to positional uncertainty

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

26 Multipath signal error Source:

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28 Positional Dilution of Precision (PDOP)

29 Obstructions to satellite signals Telescoping pole

30 Adjusting PDOP thresholds Typically want PDOP < 6

31 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

32 Types of receivers (2) Recreational receivers - $200 to $1000 Mapping grade - $ $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

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35 Differential correction

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

37 Two common types of differential GPS Best performance if base station within 180 miles, 300 km

38 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

39 CORS CORS/GoogleMap/

40 Measuring distance and azimuth angles

41 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. 45 o (northeast), 180 o (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)

42 Compass Measures azimuth angles 0º to 360º

43 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 0º is magnetic north, not geographic north Magnetic declination - angle between the compass pointing direction and geographic north, or true north

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45 /geomagmodels/struts/calc Declination

46 Distance Tape measures

47 Laser rangefinder Maximum Range Accuracy Inclinometer Range Inclinometer Accuracy 575 m 3-5 cm typical ± 90 degrees ± 0.1 deg. typical

48 Horizontal distance Want horizontal distance, or planimetric distance -- may need to slope correct Cos (θ) = hd/sd (adjacent/ hypotenuse) hd = sd * Cos (θ) B Θ can be measured with a inclinometer A Θ = inclination angle hd = horizontal distance or laser rangefinder inclinometer

49 Vertical height Some applications require measurement of height Same concepts apply B Tan(θ) = vh/hd (opposite/adjacent) vh 1 = hd * Tan(θ 1 ) vh total = vh 1 + vh 2 vh 1 = vertical height A θ 1 hd = horizontal distance θ 2 vh 2 = vertical height C

50 Measuring tree height, La Selva, Costa Rica

51 Using the Laser Tech Impulse

52 Mapping a point Sin (θ) = x/hd (opposite/ hypotenuse) x = Sin (θ) * hd Forest Cos (θ) = y/hd (adjacent/ hypotenuse) y= Cos (θ) * hd Trunk x = GPS x + x Trunk y = GPS y + y 0 N y θ x GPS control point & laser rangefinder

53 Mapping a polygon (1) Collecting corner x,y positions with a GPS receiver GPS positional error Field Plot

54 Mapping a polygon (2) Collecting corner x,y positions with a GPS receiver and differential corrections (DGPS) DGPS positional error Field Plot

55 Mapping a polygon (3) Collecting corner x,y positions with DGPS and laser rangefinder Control point DGPS positional error Laser rangefinder positional error Closure? Field Plot

56 Planning the field campaign

57 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

58 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

59 Long-term field plots

60 Field data form

61 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 vendor s 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!

62 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, /gpsdataresources.shtml

63 Data dictionary

64 GPS satellites - 02/26/2010

65 Sky plot Rohnert Park, CA 02/26/2010

66 Number of satellites Santa Rosa, CA Rohnert Park, CA 02/26/2010

67 PDOP Santa Rosa, CA Rohnert Park, CA 02/26/2010

68 Sonoma State Campus June 2007