ESS 375 Exam Review Flashcards
ARC Map
Application for making maps and analyzing data
ARC Catalog
GIS application for data management.
ARC Toolbox
Provides a reference to the toolboxes to facilitate user interface in ArcGIS for accessing and organizing a collection of geoprocessing tools, models, and scripts.
This Is How LORAN Works
Based on measuring the time difference between the receipt of signals from a pair of radio transmitters
Significance Of LORAN
Helps vessels to determine their position at sea by using shore-based radio transmitters and onboard receivers.
USNO NAVSTAR Stands For
Navigation Satellite Timing & Ranging) US Navigation system
GLONASS
GLONASS was developed by the Soviet Union as an experimental military communications system during the 1970s. When the Cold War ended, the Soviet Union recognised that GLONASS had commercial applications through the system’s ability to transmit weather broadcasts, communications, navigation and reconnaissance data.
GALILEO Stands For
Is currently the worlds most precise satellite navigation system, serving more than 3.5 billion users around the world.
BEIDOU IS
The BeiDou Navigation Satellite System (BDS) has been independently constructed and operated by China with an eye on the needs of the country’s national security and economic and social development. As a temporal-spatial infrastructure of national significance, the BDS provides all-time, all-weather and high-accuracy positioning, navigation and timing services to global users.
IRNSS Is
Indian Regional Navigation Satellite System which is an independent satellite system that is designed provide accurate position information services to users in India as well as the region extending up to 1500km from its boundary.
QZS Is
- Quasi Zenith Satellite Orbit
- Satellite positioning systems use satellite signals to calculate position information. One famous example is the American Global Positioning System (GPS); the QZSS is sometimes called the “Japanese GPS.”
Minimum Number Of Satellites Needed For Worldwide Coverage
You need 24 Satellites
Ephemerides
Gives the trajectory of naturally occurring astronomical
objects as well as artificial satellites in the sky the position & velocity over time.
Pseudorandom Code
This is an identification or ID code that
identifies which satellite is transmitting the information
This Is The Information Carried In The Almanac
Status and low-resolution orbital
information for every satellite
This Is How High Satellites Are
20,000 km
This Is Why Atomic Clocks Are Important
The atomic clocks had better frequency stability than
earlier clocks, which greatly improved the prediction of
spacecraft orbits (ephemerides) and would eventually
extend the time required between control segment
updates to GPS satellites.
This Is How Atomic Clocks Work
Every satellite needs one in order to get the time variable required for calculating position. They operate by exciting rubidium and cesium particles to create pulsating waves. The pulse rate is known and constant and allows time to be tracked through pulsating frequencies.
GPS Errors Are
Errors in the system that do not give you the correct information.
This Is What GPS Errors Cause
- Multipath Error = When GPS signals bounce off other
objects prior to receiver antenna. - User Equivalent Range Errors
This Is The Significance Of Ionspheric Delay
As GPS signals pass through the upper atmosphere signals are delayed and deflected.
- The ionosphere density varies →signals are delayed more in some places than others.
- The delay also depends on how close the satellite is to being overhead (where distance that the signal travels through the ionosphere is least).
This Is The Significance Of Atmospheric Delay
The lower atmosphere delays GPS signals, adding slightly to the calculated distances between satellites and receivers.
Signals from satellites close to the horizon are delayed the most, since they pass through the most atmosphere.
This Is What UTC Stands For
Coordinated Universal Time
DARPA Stands For
Defense Advance Research Project Agency
This Is What DARPAS Mission Is
To make pivotal investments in breakthrough technologies for national security.
Three Specific Innovations DARPA Produced
- First Satellite
- Miniaturized GPS Receivers
- GLOMR Satellite
This Is What The Escape Velocity Is For Ballistic Orbit From The Earth
11 kilometres per second
This Is How Many Satellites Are Needed To Fix A Position
4 Satellites Are Needed
This Is What A Geoid I
The shape that the ocean surface would take under the influence of gravitational field of the earth which is neither perfect nor uniform
This Is What Parity I
Its an algorithm to double check the ambiguity in time delayed signals in satellite receiver communications.
This Is Step 1 On How GPS Works
GPS satellites broadcast radio signals providing their location, status, and precise time from onboard atomic clocks.
This Is Step 2 On How GPS Works
The GPS radio signal travels through space at the speed of light which is more than 299,792km/second or roughly 300,000 km/second.
This Is Step 3 On How GPS Works
A GPS device receives the radio signals, noting their exact time of arrival and uses these to calculate its distance from each satellite in view.
This Is Step 4 On How GPS Works
Once a GPS device know it distance from at least four satellites it can use geometry to determine its location on Earth in three dimensions.
This Is The Equation For How GPS Works
Distance equals rate multiplied by time
L1 Channel
- 1575.42 MHz: Mix: the course-acquisition (C/A) and
encrypted precision P(Y) codes. - It is also used for the L1 civilian (L1C) and military (M) codes on the Block III satellites
L2 Channel
1227.60 MHz: This signal is used to carry the P(Y) code, as
well as the L2C and military codes on the Block IIR-M and later
satellites
L3 Channel
1381.05 MHz: This frequency is used to carry information
regarding any nuclear detonation (NUDET) event detected.
L4 Channel
1379.913 MHz: This signal is being studied for use with additional ionospheric correction. This would considerably improve the accuracy.
Eratosthenes, who was he, when did he live and what did he do, how did he do it?
Greek dude 2200 second century bc he correctly calculated the diameter of earth using 5 assumptions
1. the distance between Alexandria and syene is 5000 stadia
2. syeneis due north of Alexandria
3. syene is on the tropic of cancer
4. earth is a perfect sphere
5. light rays from the sun are parallel
L5 Channe
176.45 MHz: This GPS signal is being proposed for use as a civilian safety-of-life (SoL) signal.
What was the significance of Macrobius map?
Deduced north and south hemisphere symmetry
What is the significance of the Mercator world map, and what type of distortions are associated with this projection?
Navigation because it is unique in representing north as up and south as down everywhere while preserving local directions and shapes. The map is thereby conformal. Meaning that latitude and longitude were at right angle could calculate rhumb lines. Map was cylindrical, distorts area at high latitude holds shape w
What are the significant parallels of the world?
The equator (0°), the North Pole (90°N) and the South Pole (90° S), there are four important parallels of latitudes- (i) Tropic of Cancer (23½° N) in the Northern Hemisphere. (ii) Tropic of Capricorn (23½° S) in the Southern Hemisphere. (iii) Arctic Circle at 66½° north of the equator. 42N our location
What are the significant meridians of the world.
prime meridian (0)
anti-meridian (180)
we are at -84
How was longitude determined at sea prior to GPS?
John Harrison Clocks. He compared local time to port time.
How was latitude determined at sea prior to GPS?
- Any star will consistently reach the same highest
point in the sky. - Its height in the sky changes with the observer’s latitude.
- The angle the North Star makes with the horizon
(α in the figure to the right) is the same as the observer’s latitude. - Sextant - Used to calculate latitude
- Jacob staff to get an angle of
- Sun, moon, or 57 stars
Historic Navigation Aids; what were they and how did they work?
Magnetic Compass- points magnetic north when the north star is at its highest to measure the angle between celestial north and magnetic northsextant- lines up the sun with the horizon to get an angle
Two Examples Of a Projected System and Strengths and Weakness of them
- Mercator map- strength= It’s perfect for way finding; it’s the only projection for which straight lines on the map represent constant directions on the earth’s surface.
- Mercator map weakness= measurements of distance and area in its native coordinates are completely unusable.
- Lambert conformal Conic projection weakness = The primary flaw in a Conic projection is the distortion that occurs the further the image is from the standard parallel.
- Lambert conformal Conic projection strength= when we want to project countries located at mid-latitudes and with an east-west mass spread where the standard parallel is placed.
Give me two examples of coordinate systems and describe how they work.
UTM- 60 of 6 degree slices. coordinates given in northings and eastings from meridians North or South equator
Degrees, minutes, and seconds (DMS) is a format that divides the space between each line of latitude or longitude into 60 minutes and divides each minute into 60 second from meridian.
two datums why is one used over another in a certain locatoin
WGS84- few cm in error, error in Europe a lot biggerEuropean- works well with little error in Europe however US gravity is different meads Ranch- geologic surface datum calculated on the surface
Cartesian Coordinate System
lat and long works well everywhere but poles
Polar coordinate system
System that circles the poles. Distortion everywhere else
Conformality
The unique property of conformal map projections, in which all small or elementary figures on the surface of a sphere retain their original forms (shapes) on the map
Distance
- If a line from a to b on a map is the same distance (accounting for scale) that it is on the earth, then the map line has true scale.
- No map has true scale everywhere, but most maps have at least one or two lines of true scale.
- An equidistant map is one that preserves true scale for all straight lines passing through a single, specified point.
Direction
- Direction, or azimuth, is measured in degrees of angle from
north. - On the earth, this means that the direction from a to b is the
angle between the meridian on which a lies and the great circle arc connecting a to b.
Scale
- If a map preserves shape, then feature outlines (like country boundaries) look the same on the map as they do on the earth.
- A map that preserves shape is conformal. Even on a conformal map, shapes are a bit distorted for very large areas, like continents.
- A conformal map distorts area—most features are depicted too large or too small. The amount of distortion, however, is regular along some lines in the map.
Area
- If a map preserves area, then the size of a feature on a map is the same relative to its size on the earth.
- For example, on an equal-area world map, Norway takes up the same percentage of map space that actual Norway takes up on the earth.
- In an equal-area map, the shapes of most features are distorted. No
map can preserve both shape and area for the whole world,
although some come close over sizeable regions.
Geodetic Datum
An abstract coordinate system with a reference surface (such as sea level) that serves to provide known locations to begin surveys and create maps.
This Is What Tissots Indicatrix andWhat Does It Tell You
- Tool to characterize the distortion due to projecting a spherical representation of the earth onto a flat surface
- This graphic tool helps you see what type of distortion occurs in the size, shape, and orientation of ellipses that would be circles were they located on the earth’s surface.
