GIS401 – GNSS, GPS, GIS, and Remote Sensing in
Forestry
What does GNSS stand for? - Global Navigation Satellite System What does GPS stand
for? - Global Positioning System Basis of GNSS? - trilateration 4 types of
GNSS - GPS (USA), GLONASS (Russia), Galileo (EU), BeiDou-3 (China) Is GNSS a
reciever? - No What is GNSS? - constellation of earth orbiting satellites which define
geographic position on and above earths surface What three segments make up GNSS
- Satellite, Control station, receiver Different types of satellites? when are they useful?
how do they orbit? - Medium earth orbit satellites (useful for global coverage), orbit within a
defined plane
Geostationary earth orbit satellites (useful for regional coverage), orbit over the same position
on earth What type of data does a control segment upload to satellites? - ephemeris
data three elements of control segment - - monitor stations
- master control station
- ground antennas What does trilateration do? - used to identify the x,y,z coordinates
of a GNSS receiver using the geometry of spheres how many satellites are required for
trilateration? - 4 is ideal, but three is possible using the datum of the earth stored within GNSS
receiver What two data types are in a satellite signal? and what are they? - - ranging
signals (used to measure distance to satellite)
- navigation messages (includes ephemeris data) applications of GPS in forestry? - -
mapping boundaries
- mapping infrastructure and other important features
- locating features of interest
- navigation
- tracking/monitoring - workers remain 2 tree lengths away, vehicle speed monitoring, flight
path
- sensor location for remote sensing aquisition What is accuracy? - nearness of a
measurement to the true value What is precision? - variation in multiple
, measurements of the same location Different types of ranging errors that lead to
position error? - - atmospheric
- multi-path
- receiver noise
- clock and ephemeris What are atmospheric ranging errors? - - radiowaves pass
through different depths and composition of ionosphere and troposphere
- greater effect on satellites low on horizon What is multi-path ranging error? - -
receiver assumes direct path
- delays cause inaccuracy What is receiver noise error? - - unwanted disturbances that
obscure GNSS content
- thermal noise - random movement of electrons in conductor
- antenna noise - GPS receivers antenna receives electromagnetic radiation from sources other
than satellites what is clock and ephemeris error? - receiver assumes accurate
ephemeris or time of signal sent and received what is ephemeris? - lookup table of
orbital coordinates of satellites how is clock error minimised? - receiver clocks are
recalibrated often what does DOP stand for? - dilution of precision how does
DOP effect ranging errors? - increases error equation for measure of probable
accuracy? - accuracy = range error x PDOP how does satellite density impact positional
error? - Lower density = lower potential for positional error Examples of local factors
resulting in DOP? - - trees
- buildings
- mountains How are range errors and DOP affected in forests with different
characteristics? - age, stocking, canopy cover, tree height when does error in forest
increase? - - increased biomass
- decrease canopy gap size
- increase steepness what are two main causes of inaccuracy under forest cover? - -
multi-path and signal blockage what does EPE stand for? - estimate of position
error What is EPE? - level of confidence of the estimated position what rule
does the EPE follow? - 50 - 68 - 95
Forestry
What does GNSS stand for? - Global Navigation Satellite System What does GPS stand
for? - Global Positioning System Basis of GNSS? - trilateration 4 types of
GNSS - GPS (USA), GLONASS (Russia), Galileo (EU), BeiDou-3 (China) Is GNSS a
reciever? - No What is GNSS? - constellation of earth orbiting satellites which define
geographic position on and above earths surface What three segments make up GNSS
- Satellite, Control station, receiver Different types of satellites? when are they useful?
how do they orbit? - Medium earth orbit satellites (useful for global coverage), orbit within a
defined plane
Geostationary earth orbit satellites (useful for regional coverage), orbit over the same position
on earth What type of data does a control segment upload to satellites? - ephemeris
data three elements of control segment - - monitor stations
- master control station
- ground antennas What does trilateration do? - used to identify the x,y,z coordinates
of a GNSS receiver using the geometry of spheres how many satellites are required for
trilateration? - 4 is ideal, but three is possible using the datum of the earth stored within GNSS
receiver What two data types are in a satellite signal? and what are they? - - ranging
signals (used to measure distance to satellite)
- navigation messages (includes ephemeris data) applications of GPS in forestry? - -
mapping boundaries
- mapping infrastructure and other important features
- locating features of interest
- navigation
- tracking/monitoring - workers remain 2 tree lengths away, vehicle speed monitoring, flight
path
- sensor location for remote sensing aquisition What is accuracy? - nearness of a
measurement to the true value What is precision? - variation in multiple
, measurements of the same location Different types of ranging errors that lead to
position error? - - atmospheric
- multi-path
- receiver noise
- clock and ephemeris What are atmospheric ranging errors? - - radiowaves pass
through different depths and composition of ionosphere and troposphere
- greater effect on satellites low on horizon What is multi-path ranging error? - -
receiver assumes direct path
- delays cause inaccuracy What is receiver noise error? - - unwanted disturbances that
obscure GNSS content
- thermal noise - random movement of electrons in conductor
- antenna noise - GPS receivers antenna receives electromagnetic radiation from sources other
than satellites what is clock and ephemeris error? - receiver assumes accurate
ephemeris or time of signal sent and received what is ephemeris? - lookup table of
orbital coordinates of satellites how is clock error minimised? - receiver clocks are
recalibrated often what does DOP stand for? - dilution of precision how does
DOP effect ranging errors? - increases error equation for measure of probable
accuracy? - accuracy = range error x PDOP how does satellite density impact positional
error? - Lower density = lower potential for positional error Examples of local factors
resulting in DOP? - - trees
- buildings
- mountains How are range errors and DOP affected in forests with different
characteristics? - age, stocking, canopy cover, tree height when does error in forest
increase? - - increased biomass
- decrease canopy gap size
- increase steepness what are two main causes of inaccuracy under forest cover? - -
multi-path and signal blockage what does EPE stand for? - estimate of position
error What is EPE? - level of confidence of the estimated position what rule
does the EPE follow? - 50 - 68 - 95
