Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

satellite met > chapter 4: Meteorological Satellite Instumentation > Flashcards

chapter 4: Meteorological Satellite Instumentation Flashcards

1
Q

define passive radiometers

A
  • The instruments flown on-board the satellites measure electromagnetic energy that is either reflected or emitted by our planet
  • An instrument that quantitatively measures the intensity of electromagnetic radiation in some bands (wavelength regions) within the spectrum.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

basic elements of a radiometer

A

The optics, detectors, and electronics

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Optics:

A

collect the radiation, separate or disperse the spectral components, and focus the radiation to a field stop.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Detectors:

A

located behind the field stop, respond to the photons with a voltage signal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

electronics

A

That voltage signal is amplified by the electronics and converted into digital counts.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Usually, a radiometer is further identified by

A

the portion of the spectrum it covers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Usually, a radiometer is further identified by the portion of the spectrum it
covers; for example:

A
  • visible (0.4 – 0.7 um),
  • infrared (0.7 to 3.0 um – reflected IR and 3.0 to 100um – thermal IR), or
  • microwave (1 mm to 1 m).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Earth emitted radiation is detected in

A

several spectral regions by radiometers where the spectral separation through one of the following approaches.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Earth emitted radiation is detected in several spectral regions by radiometers
where the spectral separation through one of the following approaches.

A
  • Prisms separate the incoming radiation as refraction changes with wavelength (bending angle depends on index of refraction that is a function of wavelength; longer wavelengths are deflected less)
  • Band pass filters, using internal reflections within the filter, can separate the infrared spectrum into roughly 20 cm-1 segments.
  • Grating spectrometers and interferometers which are capable of spectral resolutions (λ/Δλ) of about 1/1000 also have been used for remote sensing of the earth.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

There are two common types of radiometers:

A

imagers and sounders

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Imagers:

A

A radiometer that has a scanning capability to provide a twodimensional array of pixels from which an image may be produced.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

The imagers are utilized in satellite meteorology in two ways:

A
  1. To measure the amount of visible light from the sun reflected back to space by the earth’s surface or by clouds, to produce visible imagery.
    • Visible images are the same thing we would see with our naked eye and require daylight.
  2. To measure the amount of infrared radiation emitted by the earth’s surface or by clouds, to produce ir imagery
    • Infrared images depend on the amount of radiation an object emits. The obvious advantage to having infrared capability is that weather systems can be monitored both day and night.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Sounders:

A

measure the infrared radiation, emitted by:

  • the earth’s surface or
  • by clouds,

provide:

  • vertical profiles of temperature,
  • pressure,
  • water vapor and
  • critical trace gases in the earth’s atmosphere
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

The detail visible in an image is dependent on

A
  • the spatial resolution of the sensor and
  • refers to the size of the smallest possible feature that can be detected.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Spatial resolution of passive sensors (we will look at the special case of

A

active microwave sensors later)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Spatial resolution of passive sensors (we will look at the special case of active microwave sensors later) depends primarily on their

A

Instantaneous Field of View (IFOV)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

The IFOV is

A

the angular cone

  • (A) of visibility of the sensor and determines the area
  • (B) on the Earth’s surface which is “seen” from a given altitude at one particular moment in time.
  • The size of the area viewed is determined by multiplying the IFOV by the distance (C) from the ground to the sensor.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

resolution cell

A

This area on the ground is called the resolution cell and determines a sensor’s maximum spatial resolution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

For a homogeneous feature to be detected

A

its size generally has to be equal to or larger than the resolution cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

For a homogeneous feature to be detected, its size generally has to be equal to or larger than the resolution cell.
 If the feature is smaller than this

A

it may not be detectable as the average brightness of all features in that resolution cell will be recorded.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Spectral resolution describes

A

the ability of a sensor to define fine wavelength intervals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

The finer the spectral resolution, the

A

narrower the wavelength range for a particular channel or band

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

multi-spectral sensors

A

Many remote sensing systems record energy over several separate wavelength ranges at various spectral resolutions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

hyperspectral sensors

A

Advanced multi-spectral sensors that detect hundreds of very narrow spectral bands throughout the visible, near-infrared, and midinfrared portions of the electromagnetic spectrum.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Advanced multi-spectral sensors called hyperspectral sensors, detect hundreds of very narrow spectral bands throughout the visible, near-infrared, and midinfrared portions of the electromagnetic spectrum.
 Their very high spectral resolution facilitates

A

fine discrimination between different targets based on their spectral response in each of the narrow bands.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

The radiometric resolution of an imaging system describes

A

its ability to discriminate very slight differences in energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

The finer the radiometric resolution of a sensor, the

A

more sensitive it is to detecting small differences in reflected or emitted energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Imagery data are represented by

A

positive digital numbers which vary from 0 to a selected power of 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Imagery data are represented by positive digital numbers which vary from 0 to a selected power of 2. This range corresponds to

A

the number of bits used for coding numbers in binary format.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Each bit records

A

an exponent of power 2 (e.g. 1bit=21=2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Each bit records an exponent of power 2 (e.g. 1bit=21 =2). The maximum number of brightness levels available depends on

A

the number of bits used in representing the energy recorded.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Thus, if a sensor used 8 bits to record the data, there would be

A

28 =256 digital values available, ranging from 0 to 255. However, if only 4 bits were used, then only 24=16 values ranging from 0 to 15 would be available. Thus, the radiometric resolution would be much less.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Thus, the difference in the level of detail discernible (visible) depends on

A

the radiometric resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Many electronic remote sensors acquire data using scanning systems, which

A

employ a sensor with a narrow field of view (i.e. IFOV) that sweeps over the terrain to build up and produce a two-dimensional image of the surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

multispectral scanner (MSS)

A

A scanning system used to collect data over a variety of different wavelength ranges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

There are two main modes of scanning:

A

across-track and along-track scanning.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Across-track scanners

A

scan the Earth in a series of lines. The lines are oriented perpendicular to the direction of motion of the sensor platform (i.e. across the swath).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Across-track scanners scan the Earth in a series of lines. The lines are oriented perpendicular to the direction of motion of the sensor platform (i.e. across the swath).
 Each line is scanned from

A

one side of the sensor to the other, using a rotating mirror or an array of detectors.

39
Q

Across-track scanners scan the Earth in a series of lines. The lines are oriented perpendicular to the direction of motion of the sensor platform (i.e. across the swath).
 Each line is scanned from one side of the sensor to the other, using a rotating mirror or an array of detectors.
 As the platform moves forward over the Earth

A

successive scans build up a two dimensional image of the Earth´s surface.

40
Q

…………………………………………………. determine ……………………………… and thus the spatial resolution

A

The IFOV of the sensor and the altitude of the platform determine the ground resolution cell viewed

41
Q

The angular field of view is

A

the sweep of the mirror, measured in degrees, used to record a scan line, and determines the width of the imaged swath

42
Q

Along track scanners

A
  • also called pushbroom scanners
  • along track scanners use a linear array of detectors
43
Q

Along-track scanners (also called pushbroom scanners) use a linear array of
detectors.
 Each individual detector measures

A

the energy for a single ground resolution cell and thus the size and IFOV of the detectors determines the spatial resolution of the system.

44
Q

…………………………………….. is required to measure each spectral band or channel.

A

A separate linear array

45
Q

A separate linear array is required to measure each spectral band or channel.
 For each scan line,the energy detected by each detector of each linear array is

A

sampled electronically and digitally recorded.

46
Q

Along-track scanners with linear arrays have several advantages over acrosstrack mirror scanners.

A
  • The array of detectors combined with the pushbroom motion allows each detector to “see” and measure the energy from each ground resolution cell for a longer period of time.
  • This allows more energy to be detected and improves the resolution.
47
Q

The second generation (started in 1994) GOES satellites have

A

separate imaging and sounding instruments.

48
Q

The GOES Imager

A

The imager has five channels (Table) sensing visible and infrared reflected and emitted solar radiation. The infrared capability allows for day and night imaging.

49
Q

…………………………………………………….enable imaging of an entire hemisphere, or small-scale imaging of selected areas

A

Sensor pointing and scan selection capability

50
Q

Sensor pointing and scan selection capability enable imaging of an entire hemisphere, or small-scale imaging of selected areas.
• The latter allows meteorologists to

A

monitor specific weather trouble spots to assist in improved short-term forecasting.

51
Q

The GOES Imager data are ……………………………. resolution

A

10-bit radiometric

52
Q

the GEOS imager data are 10-bit radiometric resolution, and can be transmitted

A

directly to local user terminals on the Earth’s surface

53
Q

The GOES Sounder

the …… channel sounder

A

19

54
Q

The GEOS 19 cahnel sounder measures:

A
  • emitted radiation in 18 thermal infrared bands and
  • reflected radiation in one visible band
55
Q

The 19 channel GEOS sounder measures:
• emitted radiation in 18 thermal infrared bands and
• reflected radiation in one visible band The GOES Sounder
 These data have a spatial resolution of

A

8 km and 13-bit radiometric resolution

56
Q

Sounder data are used for:

A
  • surface and cloud-top temperatures,
  • multilevel moisture profiling in the atmosphere, and
  • ozone distribution analysis
57
Q

The primary sensors on board the NOAA satellites, are the

A
  • Advanced Very High Resolution Radiometer (AVHRR) and
  • the High Resolution Infrared Radiation Sounder (HIRS)
58
Q

The AVHRR

A

It has sensor with 5 bands

59
Q

The AVHRR – It has sensor with 5 bands (Table), detects

A

radiation in the visible, near and mid infrared, and thermal infrared portions of the electromagnetic spectrum, over a swath width of 3000 km.

60
Q

AVHRR data can be acquired and formatted in

A

four operational modes, differing in resolution and method of transmission

61
Q

AVHRR data can be acquired and formatted in four operational modes, differing in resolution and method of transmission. Data can be

A

transmitted directly to the ground and viewed as data are collected, or recorded on board the satellite for later transmission and processing.

62
Q

AVHRR data are widely used for

A

weather system forecasting and analysis. The sensor is also well-suited to observation and monitoring of land features.

63
Q

AVHRR data is used extensively for

A
  • monitoring regional,
  • small-scale phenomena,
  • including:
    • mapping of sea surface temperature, and
    • natural vegetation and
    • crop conditions.
64
Q

(HIRS) is short for

A

The High Resolution Infrared Radiation Sounder

65
Q

The High Resolution Infrared Radiation Sounder (HIRS):

A

The HIRS is a scanning radiation detection sounder with 20 detectors in the infrared spectrum.

66
Q

The High Resolution Infrared Radiation Sounder (HIRS) detects and measures

A

energy emitted by layers of the atmosphere to construct a vertical profile of temperatures from the earth surface to an altitude of about 40 km.

67
Q

HIRS has ………………… channels ( ) and

A

19 infrared channels (3.8-15 µm) and one visible channel

68
Q

HIRS has 19 infrared channels (3.8-15 µm) and one visible channel. The swath width is

A

2160 km, with a 10 km resolution at nadir

69
Q

HIRS has 19 infrared channels (3.8-15 µm) and one visible channel. The swath width is 2160 km, with a 10 km resolution at nadir. HIRS uses

A

CO2 absorption bands for temperature sounding.

HIRS also measures water vapor, ozone, N2O, cloud and surface temperatures

70
Q

Microwave Remote Sensing

A

Because of their long wavelengths (1cm to 1m), compared to the visible and IR, microwaves have special properties that are important for remote sensing.

71
Q

Longer wavelength microwave radiation can

A

penetrate through cloud cover, haze, dust, and all but the heaviest rainfall, as the longer wavelengths are not susceptible to atmospheric scattering which affects shorter wavelengths.

72
Q

Longer wavelength microwave radiation can penetrate through cloud cover, haze, dust, and all but the heaviest rainfall, as the longer wavelengths are not susceptible to atmospheric scattering which affects shorter wavelengths.
• This property allows

A

detection of microwave energy under almost all weather and environmental conditions so that data can be collected at any time without interruption.

73
Q

Passive microwave sensing is similar in concept to

A

thermal remote sensing. All objects emit microwave energy of some magnitude, but the amounts are generally very small.

74
Q

A passive microwave sensor detects

A

the naturally emitted microwave energy within its field of view. This emitted energy is related to the temperature and moisture properties of the emitting object or surface.

75
Q

Passive microwave sensors are typically ……………… or …………………….

A

radiometers or scanners

76
Q

Passive microwave sensors are typically radiometers or scanners and operate in

A

much the same manner as systems discussed previously except that an antenna is used to detect and record the microwave energy.

77
Q

The microwave energy recorded by a passive sensor can be:

A
  1. emitted by the atmosphere
  2. reflected from the surface
  3. emitted from the surface or
  4. transmitted from the subsurface
78
Q

for passive microwave sensors

because the wavelengths are so ….., the ……………………………………

A

long, the energy available is quite small compared to optical wavelengths

79
Q

Because the wavelengths are so long, the energy available is quite small compared to optical wavelengths.
 Thus,

A

the fields of view must be large to detect enough energy to record a signal. Most passive microwave sensors are therefore characterized by low spatial resolution.

80
Q

Active microwave sensors provide

A

their own source of microwave radiation to illuminate the target

81
Q

Active microwave sensors are generally divided into two distinct categories:

A

imaging and non-imaging

82
Q

The most common form of imaging active microwave sensors is

A

RADAR

83
Q

The RADAR transmits

A

a microwave (radio) signal towards the target and detects the backscattered portion of the signal

84
Q

The strength of the backscattered signal is measured to

A

discriminate between different targets and the time delay between the transmitted and reflected signals determines the distance (or range) to the target.

85
Q

Non-imaging microwave sensors include

A

altimeters and scatterometers

86
Q

Radar altimeters transmit

A

short microwave pulses

87
Q

Radar altimeters transmit short microwave pulses and measure

A

the round trip time delay to targets to determine their distance from the sensor.

88
Q

Generally altimeters look

A

straight down at nadir below the platform and thus measure height or elevation.

89
Q

Radar altimetry is used on

A

aircraft for altitude determination and on aircraft and satellites for topographic mapping and sea surface height estimation.

90
Q

Scatterometers

A

generally non-imaging sensors

91
Q

Scatterometers are also generally non-imaging sensors and are used to

A

make quantitative measurements of the amount of energy backscattered from targets

92
Q

The amount of energy backscattered is dependent on

A
  • the surface properties (roughness) and
  • the angle at which the microwave energy strikes the target
93
Q

Scatterometry measurements over ocean surfaces can be used to estimate

A

wind speeds based on the sea surface roughness

94
Q

Ground-based scatterometers are used extensively to

A

accurately measure the backscatter from various targets in order to characterize different materials and surface types.

satellite met (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions