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The CloudSat Mission

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Title: The CloudSat Mission


1
The CloudSat Mission
  • CEE 6900-Environmental Application of Remote
    Sensing
  • Abel Tadesse Woldemichael

2
  • 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,

3
  • 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.
4
  • 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,

5
  • 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.

6
  • 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
7
  • 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.

8
  • 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.

9
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10
  • 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)

11
  • 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

12
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

13
  • 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

14
  • 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)
15
  • 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)

16
  • 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.
17
  • Each profile will have 125 vertical bins (slices,
    representing), and each bin will be approximately
    240m thick. ( Vertical Spatial resolution


18
FIGURE Instantaneous footprint when satellite
travels one sample period or 0.16 sec
1.1km apart
19
FIGURE effect of sliding the instantaneous
footprint along track for one sample period.
20
A CloudSat Data Granule is defined as one orbit
(which is equal to earth's circumference,
40,022km),
Vertical Resolution
21
  • 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

22
  • 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
23
THANK YOU
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