Lab 2

Lab 2 was an overview of spatial elements
( Most information and pictures taken directly from lecture slides (lecture 2 SPIT 2015) 

Points- a point has no area but is a fixed position (coordinates)
Lines- a connection between 2 or more points
Area- the space enclosed by multiple points and lines. 

Raster (see picture) 

The numbers represent a spatial value no matter how small your "pixel" is never an exact representation of actual geography

Vector (see picture)

Represented by coordinate data taken by GPS measurements x, y coordinates

GPS section- An overview of the history of gps and it's limitations


Why use GPS
(1)
•Availability:
–1995, DoD NAVSTAR, civilian use foreseeable future
•Accuracy: Factors
–work with “primary” data sources
–High inherent accuracy (2.5m medium-quality properly corrected receiver)
–Time Corrected to 1/1 billionth of a second

Differential GPS:  An extension of the GPS system that uses land-based radio beacons to transmit position corrections to GPS receivers. DGPS reduces the effect of selective availability, propagation delay, etc. and can improve position accuracy to better than 10 meters.of a second (notes) I understand this is mainly used for marine navigation I am not sure if it is useful for land based mesurements. Possibly for air. 

Sources of error

Satellite clock errors  < 1 meter

Ephemeris errors   (satellite position)  < 1 meter

Receiver errors  < 2 meters

Ionosphere errors (upper atmos.)  < 2 meters

Troposphere errors (lower atmos.)  < 2 meters

Most of these seem to be out of the users control though need to be taken into account when anomolies are found within the data. 

Multipath errors (bounced signals)  ???- seems to be the most controllable, being able to recognize areas that could potentially reflect signals causing error within how your receiver interprets them. I believe this was similar to what we were going over in the example when were taking data. The instructors had us take reading next to the building which would likely reflect the signals manipulating our data of the "square" 

Considered the most accurate representation of space with the least amount of error. (note: the distortion at the poles. The farther you get away from the equator the more distortion of information. 

Remote Sensing/Landsat 

Representing the reflection of solar radiation off the earth with satellite instruments. Multiple satellites all with different capabilities that cover different wavelengths of light. Important to note that what we see is what is not absorbed by the surface example (we see green when we look at plants due to the absorption of other light waves) Important to pay attention to the wavelengths that are covered and how often the satellite can pass over the area that you want. often takes multiple passes due to possible cloud coverage. 

landsat-etm has a 30m resolution and repeats every 16 days. 

First launch in 1972

•Landsat 1 – 7, today 5 TM and 7 ETM+ still fly

–15m, 30m, & 60m pixel resolution

–7 spectral bands, 1 panchromatic band

•3 Visible, 2 NIR, 1 MIR, 1 Thermal Low/High Gain

–Every 16 days

–Tuned for looking at the land

–Broad spectral bands

–Can “see” into estuaries and rivers