APP Flashcards
List and describe the three main areas of civil space applications
Space Applications Areas
- Satellite Communications. (Satcom, GEO)
- Earth Observation (EO, LEO)
- Satellite Navigation (Satnav, MEO)
Describe and give examples of the use of space-derived information in integrated applications
Integrated satellite applications combine SatNav, Sat comms and EO
Geo spatial services
- Integrated communication and recon
- Web mapping and GIS services
- 3D topological displays
Examples of integrated systems
- Big data analytics
- Data science
- Machine learning
List and describe different satellite missions and programs relevant for space applications and discuss the benefits and impact for users with respect to disasters, health, energy, climate, water, weather, and agriculture
SAR missions
- COSMO Skymed
- Radarsat
- TerraSAR-X
- Tandem-X
Altimetry missions
- Jason
- Cryosat
Atmospheric missions / meteorological satellites
- MetOp
- MeteoSat
Optial HR & VHR missions
- DMC
- Pléiades
- Deimos-2
- RadioEye
- SPOT (HRS)
Optical MR & LR missions
- SPOT (VGT)
- PROBA-V
Observations of the near-Earth environment
Gravity measurements and Earth interior
Climate studies (mainly LEO and GEO)
Hydrology and water cycle
Land use studies
.
.
List the merits of using space for communication, Earth observation
and navigation with their associated problems
Why Space Applications?
- Satellite applications provide essential commodities for consumers (weather, navigation, TV)
- Satellite applications are commercially viable (farmers, airplanes, etc.)
Added value of satellite applications
- Mapping large regions
- Global coverage
- Global access
- Homogenous data
- Integration
- Repeated observations
- Multi user
- Near real time
Communication satellites (GEO)
big coverage area, ability to engage radio relays in the space;
- Wireless link
- Limited bandwidth
- Noise
- Bad weather
- Low data security
- Long distance communications
- Weak signals
- Delay
- Launch and failure risks
Earth Observation (LEO)
high frequency of revolving, therefore, quick response by demand; also low altitude, therefore, good image quality
- Most complex
- Least signal latency
- Need constellation for global coverage
Navigation satellites (MEO)
at least 4 navigation satellites in various positions in space are needed to determine the position. MEO fits these conditions the best
- Less signal latency than GEO
- More complex than GEO
Explain the important terms used in the development of remote
sensing (RS) payloads and sensors.
Remote sensing is the science and art of obtaining information
about a phenomena without direct contact with it.
It deals with the detection and measurement of phenomena with
devices (Sensors) sensitive to electromagnetic energy such as:
§ Light (camera and scanners)
§ Heat (thermal scanners)
§ Radio waves (radar)
• Platform is the vehicle carrying the remote sensing device.
• Sensor is the remote sensing device that sense and record the
wavelength of energy.
.
Briefly explain the three classes of RS platforms and their
comparison (ground based, airborne and spaceborne).
.
Outline the principle of operation and the main areas of application
for radar altimeters, radar scatterometers, imaging radars (SAR)
and passive microwave radiometers.
A radar altimeter (RA), radio altimeter (RALT), electronic altimeter, or reflection altimeter measures altitude above the terrain presently beneath an aircraft or spacecraft by timing how long it takes a beam of radio waves to travel to ground, reflect, and return to the craft.
A radar scatterometer operates by transmitting a pulse of microwave energy towards the Earth’s surface and measuring the reflected energy. In space context is widely used for winds measuring.
Synthetic-aperture radar (SAR) is a form of radar that is used to create two-dimensional images or three-dimensional reconstructions of objects, such as landscapes.
A microwave radiometer (MWR) is a radiometer that measures energy emitted at millimetre-to-centimetre wavelengths (frequencies of 1–1000 GHz) known as microwaves. Microwave radiometers are very sensitive receivers designed to measure thermal electromagnetic radiation emitted by atmospheric gases.
List major design drivers at spacecraft level resulting from
accommodation and operation of major classes of remote sensor.
.
# Define the International Telecommunications Union (ITU) classifications of Global Navigation Satellite Systems (GNSS).
The allocation of frequency bands is a complex process because multiple services and users can coexist in the same range. That is, the same frequencies can be allocated for different purposes in different countries. The International Telecommunications Union (ITU) is a United Nations agency coordinating the shared global use of the radio spectrum. It involves, for instance, television, radio, cell-phone, radar satellite broadcasting, etc., and even microwave ovens. ITU has been working in the allocation of the radio-frequency bands used by the Radio Navigation Satellite Services (RNSS) where GNSS belongs to. Allocation agreements were output from the World Radio Communication Conferences in 2000 and 2003.
- GPS
- GLONASS
- GALILEO
Name systems under the GNSS and describe their basic characteristics.
.
Describe the technique of trilateration and explain its use in GNSS.
Trilateration is the geometrical problem of determining an unknown position based on the distance to the other two known vertices of a triangle (the length of two sides). In the context of space, it is used in navigation.
The GPS concept is based on time and the known position of GPS specialized satellites. The satellites carry very stable atomic clocks that are synchronized with one another and with the ground clocks. Any drift from time maintained on the ground is corrected daily. In the same manner, the satellite locations are known with great precision. GPS receivers have clocks as well, but they are less stable and less precise.
Each GPS satellite continuously transmits a radio signal containing the current time and data about its position. Since the speed of radio waves is constant and independent of the satellite speed, the time delay between when the satellite transmits a signal and the receiver receives it is proportional to the distance from the satellite to the receiver. A GPS receiver monitors multiple satellites and solves equations to determine the precise position of the receiver and its deviation from true time. At a minimum, four satellites must be in view of the receiver for it to compute four unknown quantities (three position coordinates and clock deviation from satellite time).
List several sources of error in GNSS.
• Satellite atomic clocks due to non-accurate
synchronization with the system epoch
• Ephemeris data due to miss-accuracy of orbit
determination
• Ionospheric and tropospheric delays due to different
speed of electromagnetic waves propagation,
• For ionospheric delay: longer delay observed in
the electron-rich travel path of GNSS signal -
corrected using two frequencies.
• For tropospheric delay: longer delay observed in
water vapor rich travel path of GNSS signal
- Receiver noise
- Multi-path – reflection from surrounding objects
- Jamming
.
List and define several factors that affect the performance of a GNSS.
• Satellite atomic clocks due to non-accurate
synchronization with the system epoch
• Ephemeris data due to miss-accuracy of orbit
determination
• Ionospheric and tropospheric delays due to different
speed of electromagnetic waves propagation,
• For ionospheric delay: longer delay observed in
the electron-rich travel path of GNSS signal -
corrected using two frequencies.
• For tropospheric delay: longer delay observed in
water vapor rich travel path of GNSS signal
- Receiver noise
- Multi-path – reflection from surrounding objects
- Jamming
.
.
List the diverse applications of GNSS.
Car Navigation
Personal Navigation
Ship Navigation
Aircraft Navigation
Utilization in spacecraft
Land surveying
Earth Science Applications
Crustal movement observation
Weather forecast
Agriculture.
Explain what is meant by the term ‘integrated applications’ in the space sector.
Integrated applications combine data from at least two sources and at least one is space-based, like Global Navigation (GNSS), EO data, spaceflight data. This is to benefit the environment, improve business, or promote safety, or other causes. It is to “make our lives easier” based on the user’s needs.
Explain how power transmitted from an antenna decreases with
distance.
It is described by Free-space path loss:
In telecommunication, the free-space path loss (FSPL) is the attenuation of radio energy between the feedpoints of two antennas that results from the combination of the receiving antenna’s capture area plus the obstacle-free, line-of-sight path through free space (usually air)
Formula is (Pt - power transmitted from the antenna, Pr - power received on the receiving antenna):
