The CloudSat Mission

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The CloudSat Mission

• CEE 6900-Environmental Application of Remote
  Sensing
• Abel Tadesse Woldemichael

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• Overview
• Clouds
• are not just white things that break up the
  monotony of the sky,
• Actually are the fundamental stages of cycle of
  water in the atmosphere,
• also play a crucial role in influencing our
  environment,
• Even a small change in their abundance or
  distribution can alter the climate more than the
  anticipated changes in greenhouse gases,
• How much do we know about clouds?
• Not Much!
• Our current global perspective about clouds is
  derived from spectral radiances measured by
  sensors on satellites,

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• These satellites have produced comprehensive
  pictures of global cloud cover,
• They also depict how clouds either reflect or
  hold in radiant heat energy from the sun,
• But so far we do not understand how that energy
  is distributed throughout the atmosphere,
• what we need is a tool like RADAR that can
  actually see into clouds,
• Hence, the birth of the CloudSat mission

This heat energy is what drives the planets
climate and weather
The NASA CloudSat mission uses radar in a unique
way to discover more about the interior of clouds
and hence resolving much of the unknowns about
clouds.
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• Mission Objectives
• Why CloudSat?
• It has a number of important goals in its
  mission, including
• improving weather prediction,
• help mitigate natural hazards,
• aid water resource management,
• clarify climatic processes, and
• develop critical spaceborne technologies.
• Furthermore,
• It is designed to clarify the relationship
  between clouds and climate,
• It contributes to the better understanding of
  cloud-climate feedback problem,
• Also furnish data needed to evaluate and improve
  the way clouds are parameterized in global
  models,

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• Results of CloudSat mission can help the worlds
  weather forecasters answer the following
  questions
• How much water and ice is the cloud expected to
  contain?
• How much of that water is likely to turn into
  precipitation?
• What fraction of the globes cloud cover produces
  precipitation that reaches the ground?
• Quantitatively evaluate the representation of
  clouds and cloud processes in global atmospheric
  circulation models, leading to improvements in
  both weather forecasting and climate prediction
• Quantitatively evaluate the relationship between
  the vertical profiles of cloud liquid water and
  ice content and the radiative heating by clouds.

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• CloudSat Operation
• Launch History, site and vehicle
• History
• CloudSat was selected as NASA Earth System
  Pathfinder (NASA-ESSP) satellite mission in 1999,
• CloudSat was launched on April 28, 2006,
• its primary mission is scheduled to continue for
  22 months,
• Since 2006, CloudSat has flown the first
  satellite-based millimeter-wavelength cloud radar
  (a radar that is more than 1000 times more
  sensitive than existing weather radars.)
• Launch Site
• Together with CALIPSO (another ESSP mission
  satellite), was launched from space Launch
  Complex 2W at Vendenberg Air Force Base,
  California .

the Earth System Science Pathfinder Program
sponsored missions are designed to address
unique, specific, highly focused scientific
issues, and to provide measurements required to
support Earth science research
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• Launch Vehicle
• CloudSat was launched from a two stage Delta
  launch vehicle (a vehicle that has a success rate
  of 98) with a dual payload attachment fitting
  (DPAF).
• Delta II payload Capability ranges from 2.7 to
  5.8 metric tons,
• With its payload, the vehicle stood 39meters.

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• The A-Train Concept
• The satellite will fly in orbit around Earth in a
  tight formation with the CALIPSO satellite, which
  carries a backscattering lidar,
• In turn, the two satellites will follow behind
  the Aqua satellite in a looser formation,
• As a group, the satellites have been referred to
  as the A -Train,
• The combination of data from the CloudSat radar
  with coincident measurements from CALIPSO and
  Aqua provides a rich source of information that
  can be used to assess the role of clouds in both
  weather and climate.

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• Operations
• CloudSat uses advanced radar to slice through
  clouds, (Active Sensor scenario)
• It uses millimeter wave radar that operate at
  wavelengths of approximately 3 to 8 mm (or
  frequency of 94 or 35 GHz)

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• CloudSat Operations
• Cloud Profiling Radar (CPR)
• The CloudSat payload is a 94GHz CPR developed
  jointly by NASA's Jet Propulsion Laboratory (JPL)
  and the Canadian Space Agency (CSA),
• Why 94GHz Radar Frequency (3.1 mm wavelength)?
• It was explained by NASA as a tradeoff between
• Sensitivity
• Antennae Gain,
• Atmospheric Transmission,
• Radar Transmitting efficiency.
• Sensitivity and antenna gain increase with
  frequency while atmospheric transmission and
  transmitter efficiency decrease with frequency.
• 94GHz was found to be a Good Compromise

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Other effects that come in to play with selecting
a 94GHz radar frequency areMatching the
competing and conflicting factors

• Competing Factors

• Conflicting factors

• High Vertical Resolution
• Resolving Atmospheric attenuation,
• and hence improving Sensitivity of the radar
  receiver,

• Radar Technology
• Launch constraint
• (both affecting antennae size and transmitter
  power

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• Radar Intensity is measured by a reflectivity
• factor (Z)
• Z mm6/m3
• Where
• ni No. of particles per unit volume,
• Di Diameter of particles
• Also Z is expressed in dBZ
• This is to account for very large and very small
  numbers

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• What does dBZ stand for?
• Literally
• dB decibel ( unit used to express differences
  in relative power or intensity)
• Z Reflectivity factor (amount of transmitted
  energy that is reflected back to the radar
  receiver)
• In general
• The higher the dB value the larger the object
  detected (Ex Large rain drops),
• Values of dBZlt15 usually are indication of very
  light precipitation that evaporates before
  reaching the ground.
• From this stand point original requirements on
  CPR were sensitivity defined by a minimum
  detectable reflectivity factor of -30 dBZ

(this is due to the fact that clouds are weak
scatterers of microwave radiation)
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• Other CPR Properties
• Radar sampling takes place at 625KHz
• Burst rate 0.16s/burst
• PRF 4300
• For this we can compute
• (4300 pulse/sec)(016 s/burst) 688pulse/burst
• The CloudSat antennae has a diameter of 1.85m
• It will provide an instantaneous footprint of
  approximately 1.4km (Cross Track Horizontal
  Spatial Resolution)

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• The CPR instrument will be flown in a
  sun-synchronous orbit at an 89o inclination
  angle, and a nominal altitude of 705 km. (720km?)
• This orbit character will produce an along track
  velocity of 7km/s
• Using this velocity, and the sample rate of 0.16
  sec/profile, we can approximate that a CPR
  profile will be generated every 1.1 km along
  track.

equator
polar
Sun-syn.
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• Each profile will have 125 vertical bins (slices,
  representing), and each bin will be approximately
  240m thick. ( Vertical Spatial resolution

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FIGURE Instantaneous footprint when satellite
travels one sample period or 0.16 sec
1.1km apart
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FIGURE effect of sliding the instantaneous
footprint along track for one sample period.
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A CloudSat Data Granule is defined as one orbit
(which is equal to earth's circumference,
40,022km),
Vertical Resolution
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• CloudSat Data Products
• CloudSat's standard data products include
• calibrated cloud-profiling radar reflectivity
  data, as well as
• cloud geometric profile,
• cloud classification,
• cloud optical depth by layer,
• cloud liquid water content,
• cloud ice water content,
• atmospheric radiative fluxes and heating rates,
• cloud geometrical profile with lidar input from
  CALIPSO, and
• cloud classification with lidar input from
  CALIPSO

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• Major Areas of Application
• Model-to-model variation of prediction of climate
  warming,
• Occurring as a result of the inadequate
  prediction of cloud properties and the different
  way models specify vertical climate distribution,
  
• the vertical distribution and overlap of cloud
  layers directly determine both the magnitude and
  vertical profile of radiative heating, (Graeme
  S.L)
• CloudSat has got its application in slicing
  through the cloud and finding out the radiative
  heating rate,

This heating exerts a dominant influence on the
large-scale circulation of the atmosphere as well
as on deep convective cloud systems.
Cloud Radiative Heating (K/Day) for various
thickness of clouds For example, high cloud
layers heat the tropical atmosphere by more than
80 W m-2 (relative to clear skies)
12 W/m2
45 W/m2
3 W/m2
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