Johana ChirinosMichigan Technological University

IS@AO Workshop

Ground and satellite-based night-time

cloud identification techniques

at the Pierre Auger Observatory

Identifying Clouds over the Pierre Auger Observatory

Ground-based night-time cloud identification techniques: XLFXLF and CLFCLF laser shots seen by FDs Infrared Cloud Cameras Infrared Cloud Cameras LIDARLIDARs (previous talk by Aurelio)

Satellite-based night-time cloud identification technique: GOES12/13 satelliteGOES12/13 satellite images over Southern Hemisphere

04/18/11 IS@AO Workshop 2

As part of atmospheric studies for Pierre Auger Observatory:

Identifying night-time cloudsIdentifying night-time clouds in the field of view of the Fluorescence Fluorescence

DetectorsDetectors(FD) is important for getting correct shower profilesshower profiles.

Shower profile from cosmic rays

Shower development viewed by 4FD

04/18/11 IS@AO Workshop 3

Shower profile:particles along shower path

FD pixels seeing shower profile

Clouds affecting shower profile

04/18/11 IS@AO Workshop 4

Cosmic RayShower

Attenuation of light by cloud

Decrease or absence of

fluorescence light

FD

Clouds affecting shower profile

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Cosmic RayShower

FD

Forward directed light scattered towards FD

Forward directed

light cone

CLF/XLF

• FD

04/18/11 IS@AO Workshop 6

Cloud over CLF Cloud between CLF&Eye

FD

Profile

04/18/11 IS@AO Workshop 7

IR Clouds Cameras4 IR cameras: one at each FD siteFD site.

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During FD operation:

-Full sky mosaicmosaic

27 images every 15' 15'

IR Clouds Cameras5 images across FDs field-of-view every 5' 5 images across FDs field-of-view every 5'

04/18/11 IS@AO Workshop 9

Cloud

Camera

Images

Image

Processing

FD Pixels

Cloud

Index

IR Clouds CamerasCloud-affected event

04/18/11 IS@AO Workshop 10

Cloud Camera Image

Image Processed

Satellite GOES12/13Extensive atmospheric monitoring task for many topics over 3000km2:

Great effort reat effort for constructing, running, maintaining equipment/software. For cloud identification: Satellite data will eliminate these worries. Better resolution in space and timespace and time, especially to identify exotic events.

04/18/11 IS@AO Workshop 11

Double bangCloud

Satellite GOES12/13GOES (GeostationaryGeostationary Operational Environmental Satellite) at 35,800 km.

Full-disc view of Earth: 1 visible1 visible band: 1km by 1km.

4 IR4 IR bands: 4km by 4km.

04/18/11 IS@AO Workshop 12

68-70º W longitude, 34-36º S latitude each 30' (hh09ss, hh39sshh09ss, hh39ss) at night

GOES-12/13 Imager at 75º W: Southern Hemisphere Scan Sector

4 Satellite IR BandsEmissionEmission spectrum for a 280 K black-body at Earth's surface

with absorptionabsorption effects of atmospheric water vaporwater vapor:

04/18/11 IS@AO Workshop 13

- Band 2 & 4: unaffected2 & 4: unaffected, none of earth's atmospheric gases absorb very well. , none of earth's atmospheric gases absorb very well. Able to sense Able to sense earth's surface and clouds. earth's surface and clouds.

- - BiggerBigger effect in band 3:responds to water vapor at middle and upper middle and upper layers.

Ground-truthing cloud identification technique

To ground-truth algorithm: comparison with instruments at Auger Observatory.

:

IR Cloud Camera and LIDARs:

Different field of view/timing: not easy/perfect comparison.

CLFCLF:

Cloudy/clear state of CLF pixel is regularly monitored by CLF.

Every 15' during FD nights: CLF produces 50 laser shots seen by FD.

For 2007 data, we plot all 50 laser profiles in one plot:

If peak over laser profile: Cloud over CLF

04/18/11 IS@AO Workshop 14

CLF(1 hour data)• Clear/Cloudy tag of CLF pixel: If CLF shots 9' before && 6' after bothboth clear/cloudy.

04/18/11 IS@AO Workshop 15

Satellite

07:09

07:00 Clear 07:15 Clear

07:30 Cloudy over CLF 07:45 Cloudy between CLF & Eye

Satellite

07:39

CLF pixel clear

CLF pixel undefined

Ground Temperature Correlation

For CLF pixel: T4 vs. T of ground from weather station at CLF(Tclf).

Correlation for clear nights:

T4 ~ Tclf

T4 < Tclf when cloudy.

Linear fit for clear nights:

Small residual: CLF pixel clear.

Large residual: CLF pixel cloudy.

04/18/11 IS@AO Workshop 16

T2 & T4: sensitive to temperature of emitting surface.

For clearclear pixels: T2 & T4T2 & T4 should be correlatedcorrelated with ground Tground T.

Residuals animated gifAssuming a relative uniform T of region: T of all pixels from region ~ Tclf

For every pixel: When residual small, pixel is clear(clear blue).

When residual large: pixel is cloudy(dark blue).

http://befnet.auger.mtu.edu/satellite/output/gif/All/Anim_gif_nightly/Residuals/

04/18/11 IS@AO Workshop 17

Better model of T over array: WS at CLF, at 4 FD, at BS and nearby towns.

04/18/11 IS@AO Workshop 18

Satellite info only: T3 vs T2-T4

T3 & T2-T4: independentindependent of current ground T. of current ground T.

Clear by CLF : condensed blob

Cloudy by CLF: anti-correlated line

Greatest separation between clear and cloudy.

We project data onto this line.

We fit to an empirical function of cloud probability.

Satellite info only: mapsPixels with cloud probability < 20%: light green, clear.Pixels with higher cloud probabilities in grey scale.

http://befnet.auger.mtu.edu/befnet_html/Satellite.html ATMON 2010

04/18/11 IS@AO Workshop 19

Satellite info only: maps

Cloudiness since 2007

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Ideas for a collaborative work :

We have more than 5 years of different types of atmospheric data.These could be useful to other scientists.

04/18/11 IS@AO Workshop 21

For example:Ground-truthing MODIS satellite results for a CTA site search.

Cloud Identification PrinciplesCloudsClouds are typically coldercolder than Earth's Earth's surface:

T2&T4T2&T4(non-absorbing): Sense unattenuated radiation from emitting surfaceemitting surface.

Lower T2 or T4 than Earth T: marker for clouds.

Wavelength dependence in emissivity of clouds, but not for Earth. Wavelength dependence in emissivity of clouds, but not for Earth.

Depends on relationship between cloud droplet size and wavelengthcloud droplet size and wavelength.

T2-T4:sensitive to emissivity differences for clouds between the bands.

T2-T4:T2-T4: for clouds clouds. T2 ~T4: Earth surface.

Clouds: mixture of water vaporwater vapor and liquid water droplets.

T3T3 varies with water vapor: fraction of cloudcloud in a pixel.

Cloud identification algorithms with T2, T4, T2-T4, and T3T2, T4, T2-T4, and T3 appear promising.

04/18/11 IS@AO Workshop 22