Cloud Monitor Implementa1on on the ALMA Site
for Effec1ve WVR Phase Correc1on (Conceptual Study)
Y. Asaki (ISAS) Cooperators:
M. Momose (Ibaraki Univ.), Y. Tamura (Univ. of Tokyo), T. Wada (NRO/NAOJ)
2014/06/17 1
ALMA WVR Phase Correc1on
2014/06/17 2
(Nikolik et al., 2013, A&A, 552, A104)
hVp://alma.mtk.nao.ac.jp/e/
ALMA Long Baseline Tests: Effec1veness of the WVR Phase Correc1on:
ALMA Antenna Array for Long Baseline Tests in Commissioning & Science Verification (CSV) in 2012
2-km Interferometer Phase�Black: Raw phase�Red：WVR corrected phase
2014/06/17 3
Comparison of the reality with the ALMA Specifica1on Requirements
Spatial Structure Function (RMS phase vs. Baseline length)�� Black: Raw phase� Red: WVR corrected phase� Blue: ALMA spec. requirement �����PWV: Precipitable Water Vapor�
2014/06/17 4
Effec1veness of the WVR Phase Correc1on
2014/06/17 5
2014/06/17 6
η = Φ wvr-‐corrected / Φ raw
WVR Phase Correc1on: Bad Case (PWV = 3.0 mm)
2014/06/17 7
WVR Correc1on does not work at all.
2-km Interferometer Phase�Black: Raw phase�Red：WVR corrected phase
PWV=2.0 mm
PWV=3.2 mm
2014/06/17 8
Tendency of the Effec1veness of the WVR Phase Correc1on
• PWV = 0 -‐ 0.5 mm : not work effec1vely – Because the phase is not fully fluctuated due to less amount of water vapor?
• PWV = 0.5 -‐ 2 mm : work very effec1vely
• PWV > 2 mm : work effec1vely, but some1mes fail.
2014/06/17 9
What may make the WVR phase correc1on worse?
• Instrument / Correc1on Algorithm?
• Environment (Cloud)?
2014/06/17 10
What may some1mes make the WVR phase correc1on worse?
• Instrument / Correc1on Algorithm?
• Environment (Cloud)?
2014/06/17 11
Cloud Monitor (Nobeyama Radio Observatory)
2014/06/17 12
Cloud Monitor
Cloud Monitor : Objec1ves
• To know what causes the ineffec1veness of the WVR phase correc1on.
• If we find a correla1on between clouds and ineffec1veness… – WVR phase correc1on status can be predicted by the cloud monitor.
– We can judge if WVR phase correc1on shall be applied or not from the cloud monitor image.
2014/06/17 13
Cloud Monitor at Nobeyama
Radio Observatory
(Infrared Camera)
2014/06/17 14
We can make use of the heritage of the technologies of cloud monitors used in previous site surveys.
Specifica1on Requirements
• To detect clouds covering the AOS site with the PWV of a few mm.
2014/06/17 15
Wave Length 8 – 12 μm (COTS Camera)
Imaging Area (Zenith Angle) 0 – 70 deg
Imaging Speed 1 frame / 1 min
Sensi1vity 2 mm PWV (1-‐min Average)
Atmospheric Transmission (ATRAN: hVps://atran.sofia.usra.edu/cgi-‐bin/atran/atran.cgi)
2014/06/17 16
5000 m Al1tude
Mid-‐Infrared Camera: Commercial Off-‐The-‐Shelf Product
2014/06/17 17
Schedule
2014/06/17 18
2014 Jun – 2014 Dec Design and Purchase of Parts
2015 Jun – 2015 Dec Manufacture
2016 Jan – 2016 Mar Implementa1on at AOS
2016 Apr – Monitor Test & Opera1on
Rough Cost Es1ma1on (5.5M JPY)
2014/06/17 19
Design and Manufacture 3M JPY
Shipping Cost 0.5M JPY (Japan to Chile)
Implementa1on and Adjustment at AOS
2M JPY (2 persons X 1 month)
Opera1on Cost 0 (Maintenance Free)
( 1M JPY ~ 10,000 US$ )
Thank you.
2014/06/17 20
