Lecture 5

Question 1

Aircraft features

Answer 1

– Very convenient
– On-board repairs possible
– Range of altitudes from meters to kilometers
– Speed:0–300m/s
– Height determines scale, coverage, & resolution
– Speed determines linear sampling rate

Question 2

Aircraft: Key Parameters

Answer 2

POSITION (electronic navigation system) various ground and satellite stations

GROUND CONTROL POINTS (GCPs)–reference points for coordinates

ATTITUDE inertial navigation system (INS)

Question 3

Aircraft: inertial navigation system (INS):

Answer 3

For measuring attitude in aircraft

INS is a navigation aid that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate via dead reckoning the position, orientation, and velocity (direction and speed of movement) of a moving object without the need for external references.

Question 4

Aircraft electronic navigation systems (5 examples)

Answer 4

Ground stations, etc

OMEGA: Ground based radio transmitter
Loran: Ground based radio transmitter
GLONSS: Satellite based radio transmitter
Galileo: Satellite based radio transmitter
GPS: Satellite based radio transmitter

Question 5

Ground Control Points (GCPs)

Answer 5

Use as reference point for known coordinates, e.g. to look at change over time

– Natural features of known location
– GCPs should not have a tendency to change over time, examples for ideal GCPs are: road intersections and airport runways
– Marker on the ground

Question 6

Satellites: disadvantages and advantages

Answer 6

Advantages
– Increased platform speed
– Continuity of missions
– Better data coverage
– Homogeneous data collection
– No political boundary issues

Disadvantages
– On-board repairs difficult or impossible
– Sampling constrained by orbital geometry

Question 7

Fundamentals of Orbital Mechanics

Answer 7

see slide for formulas

Gravitational Force (F)
Centrifugal force (Fc)
Kinetic Energy (KE)
Potential energy (U)

Velocity to maintain a stable orbit
Velocity to escape Earth’s gravitational field

Question 8

Points in RS history

Answer 8

• understand EMR
• Applied physics to develop equipment like camera
• Build up of new platforms (e.g. microwave sensors)
• Collaboration between science, defense, and commercial led to huge development (e.g. move from M to cm)

Question 9

Ibn Alhaitham (965 C.E. in Basra, Iraq)

Answer 9

father of optics–described eye, camera obscura, optics, physics, etc

Question 10

Platforms for remote sensing

Answer 10

see slide for heights

Camera
Scanner
Radar
Passive Micro radiometer

Question 11

Launch and Maneuver of Satellites

Answer 11

see slide

Question 12

Orbit Geometry

Answer 12

see slide

Question 13

Orbital time (nodal period)

Answer 13

Time required for a satellite to complete one revolution about the Earth
• For a stable orbit around Earth, this depends only on the height of the satellite
(see slide)
T0 = orbital time in seconds
Rp = planet radius (6380 km for Earth)
H = orbit altitude
gs = gravitational acceleration at the surface 9.81 m s-2

Question 14

Orbital geometry: Ascending (Descending) pass

Answer 14

– Path followed by the satellite as it moves from south to north (north to south) in its orbital trajectory

(night or day)

Question 15

Orbital geometry: Inclination

Answer 15

– Angle made by the ground track of the satellite in relation to the Equator on its ascending pass
– Less than 90 degrees is a PROGRADE orbit (in direction of rotational motion)
– Greater than 90 degrees is a RETROGRADE orbit (opposite rotational motion)

Question 16

Height of geostational orbit

Answer 16

35,000 km

Question 17

Orbital decay

Answer 17

• Orbits decay with time and often need to be boosted with small rocket thrusts
– Due to the atmospheric friction the LANDSAT 5 satellite descends by about 5 m/day

Question 18

Description of orbits

Answer 18

All satellites have an elliptical orbit with the Earth’s center as one focus
• The extent to which an orbit is elliptical or circular is defined as its eccentricity (e)
Description of orbits
e  ra  rp ra  rp
rp = radius at perigee ra = radius at apogee
• Often the orbit is close to a circle with an eccentricity (e) of 0

Question 19

in-class questions: Explain Plank’s law

Answer 19

Every body that has temp greater than 0 Kelvin emits radiation. Gives us amount of radiation emitted from a blackbody along EMR spectrum DEPENDS ON TEMP, for each wavelength. Plots emittance by wavelength

Question 20

in-class questions: what is steffan-pulse? Law

Answer 20

total amount of E emitted by blackbody is function of temp

Question 21

Hertz

Answer 21

one cycle per second, 1/s