CLOUD MONITORING WITH CCD's by liuhongmei

VIEWS: 21 PAGES: 36

									          TASCA
the Tololo All-Sky CAmera
   Hugo E. Schwarz, Roger Smith,
          & David Walker
            March 2000
        What is TASCA?
     • Whole sky images 1800 times per night
       • Nikon f/2.8 8mm 180° fisheye lens
       • FLI wheel with B, R, Na, Hg filters
for clouds, airglow, sodium & mercury light pollution
       • FLI 1k² CCD camera and controller
               • Image acquisition PC
               • Image processing PC
   • Software, including website & data archive
         • Software for image animation

               TASCA - Tololo All-Sky CAmera            2
                       System layout
Web                                                              ~$2.5K
JPEG
                 Server        $2K
                   &
                                                            Camera       $7.5K
               Acquisition                    53m
                                                          Weatherproof
  200GB
                                                           enclosure
                                                                          ~$300
               In 0.9m                              Across road
                                  100baseT
              telescope                              near 0.9m
                                                     telescope
  Solaris
  / Linux

  Client
Workstation


                          TASCA - Tololo All-Sky CAmera                    3
 TASCA
camera &
  lens




 CD for scale   TASCA - Tololo All-Sky CAmera   4
Dome

                                                    TASCA
                                                    housing


       Air inlets

         Lens
  Powersupply

100 peso coin

  Filter wheel
                    TASCA - Tololo All-Sky CAmera             5
TASCA pillar                                Jorge Briones



Housing


3m pillar




  Ladder
            TASCA - Tololo All-Sky CAmera         6
                                Vicuña



 TASCA
placement

Serena



             •
                                                 Pachón
Coquimbo




 Andacollo          Ovalle




                 TASCA - Tololo All-Sky CAmera       7
TASCA location


                                          10km




      TASCA - Tololo All-Sky CAmera   8
System components
    Lens:          Nikon 8mm f2.8 Fish Eye
    $2.5K          23 mm image circle


     CCD:          1024x1024 pixels
   $7-15K            @ 24um / pixel=0.18°
(including         Thermoelectrically cooled
controller)        Dark current: 5 - 30 e-/s
                   Read Noise     7 - 15 e-

      TASCA - Tololo All-Sky CAmera       9
FLI - SITe1024

              •   $7500 due to SITe sale
              •   RON=7 e-, 100 KHz
              •   < 5” x 5” footprint
              •   Dark only 5 e-/sec
              •   <500’ ethernet cable
                  to laptop via
                  parallel port adapter
  TASCA - Tololo All-Sky CAmera      10
         Disk space calculation...
Image size:      512 x 512
          at 2 bytes / pixel = 0.5MB
  compressed by 3, losslessly.
Acquisition rate: 3 frames/ minute = 0.5MB/min
Store:                every image in long term
Dark time:         10 hours per night, on average
Moonless for       50 % of time.
Total images p.a. = 312.000 = 52GB compressed
                            = 150GB full.
               2x 80 GB disks stores full year

               Removable 80GB disks for archive

                     TASCA - DVDs CAmera
             until burningTololo All-Skybecomes cheaper   11
         Outline of TASCA
• Why optical detection instead of IR ?
• Cloud detection
• Light pollution monitoring
• Aircraft tracking & predicting (PASCA)
• Meteorite tracking & finding (CASCA?)
• 900km baseline, track……..??? (EASCA? At Paranal)




                  TASCA - Tololo All-Sky CAmera      12
     Cloud detection methods

Contrast is provided by…..
• Thermal emission, typically at 8-12 um
• Extinction of airglow, at 1-2 um
• Extinction of starlight & airglow, 0.4-1 um




                 TASCA - Tololo All-Sky CAmera   13
     Advantages of thermal IR
        Clouds detectedstructureless. to
         so Clear sky is equally well
             important is this, given that
...but howno mechanism is required in clouds
       starlight, bythe sun or and moonlight
              occult eye in and daylight.
  are easily seenmoonlightsunmoon




               TASCA - Tololo All-Sky mid
     (Images from APO’s CAmera IR Scanner) 14
Disadvantages of thermal IR
• High (cold) clouds are harder to detect.
• Extinction not quantified.
• Expensive
• All sky coverage is problematic/expensive.
• Light pollution monitoring lost

               TASCA - Tololo All-Sky CAmera   15
 All sky coverage options...
• Custom silicon fish eye …$$$$
• Gold hemispherical reflector
 ….problem keeping emissivity low.
• Array with pan/tilt + software

• Raster scanned photometer, such as….


            TASCA - Tololo All-Sky CAmera   16
     Apache Point All Sky Camera
    Dual mirrors scan single channel photometer
         across whole sky every 3 minutes
                           Fast scan
electronics
                            mirror

supplies
         Cost ~100kUSD                                Stationary HgCdTe
                                                      tuned for 10-12 um,
                                                      liquid N2 cooled.

                                 Slow scan
                                   motor
            (prior to final packaging)
      http://galileo.apo.nmsu.edu/sky/irsc/
                          TASCA - Tololo All-Sky CAmera             17
      So………. CCD’s
• 10 times cheaper.
• Greater spatial resolution
  with no moving parts
• Higher time resolution

• Measures extinction directly.
• Images air glow, if desired.
• Light pollution monitoring
             TASCA - Tololo All-Sky CAmera   18
      Cost is driven by
 pixel scale & field of view
What spatial resolution is required?

   Let’s review some examples of
     cloud textures from the US
  National Weather Service’s photo
               library

           TASCA - Tololo All-Sky CAmera   19
     Cumulonimbus

Fortunately we don’t often have
clouds that are this easy to see.




         TASCA - Tololo All-Sky CAmera   Mauna Kea!
                                                 20
     Cirrus Unicus




These wisps are thin compared to
        o
the 0.18 pixels used in our tests.

        TASCA - Tololo All-Sky CAmera   21
                Thin Altocumulus




But this spatial scale
and contrast should
be easy to detect. TASCA - Tololo All-Sky CAmera   22
Thick Altocumulus




Uniform cloud should be easily
detected if thick enough since
we can quantify extinction
       TASCA - Tololo All-Sky CAmera   23
Thin altocumulus




                 When cloud is thin and
                coverage fairly uniform,
                      higher resolution is
              probably needed to detect
                  motion of fine texture.
    TASCA - Tololo All-Sky CAmera          24
Use animation to distinguish
clouds from structure of sky.
 Minimum animation requirements:
   –   15 Hz
   –   at 5122
   –   no jumps (skipped frames)
   –   no pauses
   –   no “sparklies” or other artifacts

              TASCA - Tololo All-Sky CAmera   25
Direct cloud movie.




    TASCA - Tololo All-Sky CAmera   26
Suppress structure of clear sky
• Divide by clear sky reference on disk to
  show extinction, scattering & airglow

• Reference image will be median of
  previous nights at same sidereal time,
  excluding moon & twilight.
     ….Unnecessary when moon is up ?


               TASCA - Tololo All-Sky CAmera   27
Extinction movie.




   TASCA - Tololo All-Sky CAmera   28
         Detection limits
           for the test camera
For static image:
 10% extinction over 0.2 FOV
                         o


 2% extinction over 1            o
                                        FOV
…better than this for animation




            TASCA - Tololo All-Sky CAmera     29
    Air glow




TASCA - Tololo All-Sky CAmera   30
Aircraft movie




  TASCA - Tololo All-Sky CAmera   31
         Identified Flying Objects
            Smaller pixels & shorter exposures
           would be better for aircraft detection
10 arcmin/pix                    2 arcmin/pixel
                Aircraft

   5 sec exp                   25 sec exposure

2 arcmin/pix

                                         Satellite
  Meteor
                                                     track
                                                             flare
                     TASCA - Tololo All-Sky CAmera             32
Discourage local light pollution




          TASCA - Tololo All-Sky CAmera   33
        Distant light pollution
•   Twice per night set of Na & Hg images
•   Before and after legal switch-off time
•   Separate street and commercial lighting
•   Monitor in-night, medium & long term
•   Line of sight to all major polluters
•   Sky brightness monitoring…..not easy.

                 TASCA - Tololo All-Sky CAmera   34
              Conclusions
• CCD’s detect thin clouds, airglow, light
  pollution (local & distant), aircraft,
  meteorites, extinction, + ???????
• ~$10-15K …much cheaper than IR
• Simple, few moving parts
• Off the shelf components
• Modest software development
•          (simpler than IR solution)
               TASCA - Tololo All-Sky CAmera   35
Outreach
             •    zodiacal light setting
             •    sky rotating full circle
             •    planets wandering
             •    the eventual comet
             •    meteor showers
             •    light pollution

TASCA - Tololo All-Sky CAmera          36

								
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