Satellites

what are satellites

objects that revolve around another object

what is an example of a natural satellite

the moon

what are orbits

the REPEATING path that one object takes around another

why are satellites used for remote sensing

1. view from a high altitude so harder to shoot down

2. has regular visit times at locations due to the repeating path

3. large areas are covered quickly

4. synoptic (broad) view of the landscape

   1. automatic image gathering (we don’t need to be there to take photo)

what kicked off the Space Race

Russia launching the first artificial satellite

what is an orbit cycle

the interval of time required for a satellite to pass a point on earth’s surface directly below the satellite for a SECOND time

what is key about a satellites orbit cycle

the satellite passes the same point TWICE

what causes the orbit cycle of a satellite to vary

1. altitude

2. velocity of the orbit

what is revisit time

the interval of time between observations of the same point on earth bu a satellite

Compare orbit cycle and revisit time

orbit cycle refers to the time it takes for a satellite to complete one full orbit, revisit time is the time it takes for a satellite to return to the same area and image it again

what causes revisit time to differ from orbit cycle

temporal resolution - revisit time differs because satellites can look off nadir

what are the types of orbits

1. geostationary orbit

2. near polar obits

3. sun synchronous

what is the geostationary orbit

an orbit that matches the speed and direction of the earth’s rotation so the satellites appear stationary

how long does it take a geostationary orbit to complete one orbit

about 24 hours

what is an example of why geostationary orbits are used

for continuous data collection over one location - weather satellite

what are advantages and disadvantages of geostationary satellites

advantages

• stationary location relative to the planet (know info about specific locations)

• high temporal resolution

• tracking from the ground is simple

disadvantages

• radio signals lag due to high altitudes

• incomplete coverage of the planet

• satellites along the equator will have poor coverage past 60 degrees latitude

what are near orbit satellites

an orbit path close to the north and south poles

describe the path of a near polar orbit

follow a north to south path while the earth rotates near polar orbits west to east

what near polar orbits are considered descending? ascending?

descending = orbits from north to south

ascending = orbits from south to north

what are the types of remote sensing orbits

near polar and sun synchronous

what are sun synchronous orbits

an orbital path set so the satellite crosses the same area at the same time therefore the sun’s position in the sky will always be the same within the same season

when are sun synchronous orbits imporant

for monitoring changes between images

what is swath width

the width of the ground area a satellite views

what does the swath width vary upon

the sensor

what are two kinds of satellite scanners

across tracker scanners

along track scanners

across track scanner

a scanning method that uses a rotating mirror to collect data by moving BACK and FORTH

what is an along track scanner

a scanning method that uses a linear array to collect data directly on a satellites path

what type of scanner is coined whiskbroom

across track scanner

what type of scanner is coined push-broom

along track scanners

contrast the scan direction for across and along track scanners

across - lines are perpendicular to the direction of the satellite

along - lines are parallel to the direction of the movement

describe how the internal detectors of along and across scanners differ in their sensitivities to wavelengths

across - sensitive to specific ranges of wavelengths

along - sensitive to specific ranges of wavelengths within ONE ground cell

what track scanner has a longer dwell time? shorter?

across scanner - short dwell time

along scanner - long dwell time

what is an example of a satellite that uses across track scanners

Landsat TM

what is an example of a satellite using along track scanners

landsat 8

what is relief displacement

the idea that objects towards the edge of an image appear to lean away

what is tangential scale distortion

the compression of image features at points AWAY from nadir

what is off nadir viewing

the capability in which a sensor is not fixed to sense directly below which shortens the revisit time

where are two tracking satellite stations in Canada

prince alberta saks and gatineau quebec

what are the four types of resolution

1. spatial

2. radiometric

3. spectral

4. temporal

contrast the four types of resolutions

spatial - smallest unit of area the sensor can collect info about

radiometric - sensor’s ability to determine fine differences in a band of energy measurements

spectral - the number and width of bands measured by a sensor

temporal - the revisit time (time between images in the same location)

what satellite system has the longest record of continuous monitoring

Landsat

what is the gold standard of satellites

Landsat

compare the number of bands in Landsat satellites

started with 4 bands before increasing to 7 then 8 then 11

compare the bit data in Landsat satellites

started as 6 bit data then increased to 8 bit then 12 bit

compare the spatial resolution in Landsat satellites

started with resolution of 79 m then deceased to 30 m with a thermal band of 120 m then decreased to a 60 m thermal band and a15 m panchromatic band

compare the temporal resolution in Landsat satellites

started as 16 days and remained constant unless Landsat 8 and 9 are combined then it decreases to 8 days

describe the type of scanners in Landsat satellites

all had across track scanners except Landsat 8 and 9

what band was added in the Landsat TM satellite that distinguishes it from the Landsat MSS

the thermal band

what band was added in the Landsat EMT+ satellite that distinguishes it from the Landsat TM

the panchromatic band

what is a panchromatic sensor

a sensor that measures one broad range of wavelengths

what is pan sharpening

the process of merging high resolution PANCHROMATIC and lower resolution MULTISPECTRAL imagery to create a single coloured image

what happened to Landsat 7 and caused it to be decommissioned

a broken scan line corrector caused gaps in the data collection

what are two sensor designs in Landsat 8

Operational land imager (OLI)

thermal infrared sensor (TIRS)

what were the two bands that distinguish Landsat 8 and 9 from the other satellites

band 1 (ultra-blue)

band 9 (cirrus cloud detection)

were landsat 9 sensors designed to match landsat 7

NO - match landsat 8

contrast the OLI-2 and TIRS-2 Landsat sensor designs

OLI - along track sensor with a 15 degree filed of view

TIRS - along track sensor with two thermal imaging sensors

what is the ultra blue band used for

measuring chlorophyll concentrations in costal regions

what is the cirrus band for

to identify where high, thin cirrus clouds are to identify interference with measurements

how do Landsat 8 and 9 detect cirrus clouds

by measuring reflected NIR energy

how does the amount of emitted thermal radiation differ

the object’s temperature

does everything emit thermal infrared radiation

yes

what was landsat 9 built with

redundant counterparts for critical components to ensure continued collection of data remains scientific grade

what is SPOT

a satellite system that has a commercial orientation rather than experimental like Landsat

what is the second longest earth observation mission

SPOT

what are SPOT satellites capable of

off nadir viewing which allows for shortened temporal resolution

what satellite system can createt digital elevation models

SPOT

what happens when satellites view off nadir

createt a parallax

type of satellite orbit in SPOT satellites

sun synchronous and near polar

type of track scanners in SPOT satellites

along track sanner

what is the revisit time for SPOT satellites

between 1 and 3 days

why is revisit times short for SPOT satellites

because they can look off nadir

what satellite system is operated by the European Space Agency

sentinel

what are examples of uses of sentinel satellites

land monitoring

emergency management

security

compare the number of bands in sentinel 2 and 3

sentinel 2 - 13 bands

sentinel 3 - 21 bands

compare the bit data in sentinel 2 and 3

sentinel 2 - 12 bit

sentinel 3 - 14 bit

what track scanner are sentinel satellites

along track scanner

what was the first high resolution satellite system to be publicly owned

Digital Globe

what type of orbit do Maxar satellites have

non-synchronous

what are uses of Maxar satellites

generates 3d world models for military and envi monitoring

what are the three satellite types in planet labs

dove

rapideye

skysat

what is unique about planet lab satellites

much much smaller than the Landsat and other satellites

how are dove planet lab satellites launched

in flocks between 28 or 30 satellites

how do planet lab’s dove satellites orbit

these satellites align in a straight line and follow each other to scane the earth every day

what kind of filters do dove sensors use

a bayer pattern filter or a Butcher block filter

describe a Bayer pattern filter in the dove satellites

top half blocks NIR wavelengths to receive RGB wavelengths and the bottom half blocks RGB to receive NIR wavelengths

then the frames are combined with adjacent frame to generate a 4-band image

describe the butcher block filter in newer dove satellites

have 4 individual pass band filters that separate light into blue, green, red and NIR channels