We examine the experiences and ideas from operating observatories regarding the measurements of the characteristics of the atmosphere that must be gathered within the locality of the observatory in order to support safe, efficient and scientifically optimized observatory operations as well as commissioning, performance monitoring and support the scientific analysis of telescope observations. We describe the expected requirements for the measurement capabilities of the the TMT Site Conditions Monitoring System (SCMS) and discuss how these plans are being developed with input from staff at operating observatories and active observational astronomers

Skidmore, Warren

Travouillon, Tony

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The Thirty Meter Telescope Site Conditions Monitoring System
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2015 J. Phys.: Conf. Ser. 595 012033
(http://iopscience.iop.org/1742-6596/595/1/012033)
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The Thirty Meter Telescope Site Conditions
Monitoring System
Warren Skidmore & Tony Travouillon
Thirty Meter Telescope, 1111 South Arroyo Parkway, Suite 200, Pasadena, CA 91105, USA
E-mail: was@tmt.org
Abstract. We examine the experiences and ideas from operating observatories regarding
the measurements of the characteristics of the atmosphere that must be gathered within
the locality of the observatory in order to support safe, efficient and scientifically optimized
observatory operations as well as commissioning, performance monitoring and support the
scientific analysis of telescope observations. We describe the expected requirements for the
measurement capabilities of the the TMT Site Conditions Monitoring System (SCMS) and
discuss how these plans are being developed with input from staff at operating observatories
and active observational astronomers.
1. Introduction
The Thirty Meter Telescope Project moved into the construction phase in May 2014. The
nominal time for the end of construction and beginning of early science operations and full
commissioning is 2024. At the end of construction the present plan calls for a multiple laser
guide star system supporting a fully functioning MCAO system. The MCAO system will feed
a dual channel diffraction limited NIR imager and IFU instrument and an AO enhanced NIR
multi-object spectrograph. An optical seeing limited wide field optical spectrograph will be
available. Both classical and queue scheduled observing modes will be provided. Commission-
ing will include optimizing the AO system, developing observing and data reduction procedures
and optimizing the image quality through the use of the enclosure vents.
The present plan for the SCMS is based on the TMT site testing system [2] (see Section 2).
However a system to evaluate a site for an observatory has different requirements to a system
that supports observatory operations and commissioning. It is important to explore the require-
ments for the TMT SCMS.
The TMT SCMS will work in a complimentary way with the Engineering Sensor (ESEN)
system. The ESEN consists of many air and structural temperature probes, sonic anemometers,
precipitation and humidity sensors, accelerometers to measure vibrations and tilt meters to
measure structural deformations on and around the telescope.
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Journal of Physics: Conference Series 595 (2015) 012033 doi:10.1088/1742-6596/595/1/012033
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2. Present Requirements for the SCMS
The TMT SCMS is required to support all of the commissioning and operations activities as
well as provide input for local conditions forecasting and provide astronomers with information
on local conditions during their observations to enable treatment of systematic effects in their
astronomical data that may limit interpretation.
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ARCH. SITE
PLAN
AS101
E.J.G.
J.T.U
11-22-2011
SCALE:  1" = 20'-0"
ARCHITECTURAL SITE PLAN
1 200'-0" ENVIRONMENTAL AREA RADIUS
2 PROPOSED DISTURBED SITE AREA LIMITS
3 VEHICULAR GUARDRAIL
4 TMT STAFF PARKING
5 CIRCULATION PATH (CENTERLINE)
6 NATURAL LANDSCAPING
7 2" DECOMPOSED GRANITE OR CRUSHED BASALT
8 TMT ACCESS ROAD
9 SITE DRAINAGE SWALE
10 SITE DRAINAGE SWALE OUTLET
11 49'-0" X 49'-0" DOME CRANE ACCESS
12 TRUCK ACCESS TO FIXED ENCLOSURE BASE
13 TRUCK ACCESS TO SUPPORT BUILDING
14 DISTURBED AREA TO BE GRADED SIMILAR TO THE EXISTING SITE CONTOURS
TO CREATE A MORE NATURAL SURFACE
15 CONCRETE WALK
16 UNDISTURED AREA OF THE SITE
17 WEATHER STATION TOWER (N.I.C.)
18 CONCRETE DRIP PAD FOR DIESEL FUEL REFILLING - SEE SB102
19 HELCO PME-6 MEDIUM VOLTAGE SWITCHGEAR
20 HELCO SERVICE TRANSFORMER
21 ELECTRICAL SERVICE ENTRANCE SWITCHBOARD
22 ATMOSPHERE TURBULANCE MONITOR (N.I.C.)
23 CONCRETE CONTAINMENT PAD AND FILL STATION FOR DIESEL FUEL TANK
24 STEEL PIPE BOLLARD BARRICADE IN FRONT OF UTILITY EQUIPMENT
25 TMT VISITOR PARKING
26 UNDERGROUND WASTE STORAGE TANK
27 UNDERGROUND DOUBLE CONTAINED CHEMICAL STORAGE TANK
28 UNDERGROUND FIRE WATER STORAGE TANK
29 UNDERGROUND DOMESTIC WATER STORAGE TANK
30 ELECTRICAL PULL BOXES - SEE ES101 FOR TYPE
GENERAL INFORMATION
PROPOSED LOCATION
MAUNA KEA SCIENCE PRESERVE
ASTRONOMY PRECINCT
AREA "E" - 13 NORTH
PROPOSED SITE ELEVATION
FINISH GRADE ELEVATION = 13,161'-0"
PROPOSED DISTURBED SITE AREA
AREA: APPROXIMATELY 4.5 ACRES
  (3.9 ACRES BEFORE RE-CONTOURING)
PROPOSED BUILDING SIZE
52,679 GROSS SQUARE FEET
SINGLE LEVEL FACILITY
(OVERALL FOOTPRINT OF THE FIXED ENCLOSURE
BASE AND SUPPORT BUILDING)
PROPOSED SITE GRADING
CUT: 36,882 CUBIC YARDS
FILL: 22,356 CUBIC YARDS
NET: 14,526 CUBIC YARDS CUT
020'-0"
1" = 20'
10'-0" 40'-0"20'-0"
Figure 1. Plan of the TMT observatory at the its on Maunakea, showing the location of the
SCMS (circled near top middle) with the measured wind rose super-imposed over the location
of the telescope pintle bearing.
The location of the main part of the SCMS will be quite close to the observatory, see Figure 1
and the validity of local seeing measurements will be significantly reduced. The main components
of the site testing system were a MASS/DIMM to monitor the atmospheric turbulence profile and
integrated seeing, an All-Sky Camera (ASCA) for cloud and light pollution measurements [4], an
Automated Weather Station (AWS) with a full suite of typical meteorological instrumentation,
Sonic Anemometers at many locations around the observatory and an Infra-Red radiometer
(IRMA) device to measure the PWV [1]. Sonic anemometers have been baselined as both wind
and optical turbulence sensors [5] to be located around the telescope enclosure vents, working
with sonic anemometers located on the telescope itself so that the optimal vent configurations
can be derived to give the best image quality for a given set of external wind and temperature
conditions and to help diagnose image quality problems that may or may not be related to wind
flow through the enclosure.
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Journal of Physics: Conference Series 595 (2015) 012033 doi:10.1088/1742-6596/595/1/012033
2
3. Re-examining the SCMS Requirements
3.1. Information Gathering
A lot of communications were carried with operations staff at the Gemini North, Paranal, IRTF,
CFHT and Keck observatories, with astronomers that use AO corrected images for extremely
precise astrometric measurements, mid-IR spectroscopic and seeing limited optical observations
and with meteorologists that make forecasts of the astronomical observing conditions for
Maunakea. All were asked what types of atmospheric measurements are required for their
specific needs. Where appropriate specific requirements were extrapolated or adjusted for the
TMT.
3.2. Telescope Operations
In telescope operations the SCMS measurements would be used for optimizing queue scheduled
observations, e.g to decide whether to follow or change the plan of scheduled observations.
To do this would require the measurements listed in Table 1. Also listed in Table 1 are the
measurements needed to ensure safe telescope operations and to support the segment alignment
process because segment alignment works best during periods of good seeing.
Table 1. List of SCMS measurements needed for telescope operations, commissioning and
performance monitoring and supporting scientific analysis.
Queue implementation and Clouds, transparency, sky brightness, PWV, seeing
forecasting support Turbulence profile if using AM2
Wind speed and direction
Optimized telescope performance Wind speed and direction
(wind shake, vents, pointing)
APS operations (M1 alignment) R0 and seeing
Telescope safety Fog, dust, wind speed and direction, humidity
Dew point (air pressure, temperature, humidity)
Solar radiation
MCAO performance estimation R0, seeing, turbulence profile
and monitoring Wind speed and direction
Seeing limited instrument Transparency, cloud cover, seeing
performance evaluation
Scientific interpretation Wind speed and direction, air temperature, air pressure
Sky brightness, PWV, seeing, transparency
Turbulence profile
Another important aspect of SCMS support of operations is the supporting of conditions
forecasting by providing information on observing and atmospheric conditions to the enable
anchoring of forecast models and fine tuning. The Mauna Kea Weather Center carries out this
work and continually seeks to improve the quality of forecasts and respond to the needs of the
observatories on Maunakea.
3.3. Commissioning and Performance Monitoring
Observatory commissioning must be carried out whilst ensuring the safety of the telescope and
other equipment. A good understanding of the atmospheric characteristics will greatly enhance
Adapting to the Atmosphere Conference 2014 IOP Publishing
Journal of Physics: Conference Series 595 (2015) 012033 doi:10.1088/1742-6596/595/1/012033
3
the ability to isolate and diagnose problems that all ultimately affect image quality. Understand-
ing the fundamental expected image quality due to the atmosphere and being able to identify
the cause of any degradation, be it due to incorrect AO correction, wind induced image jitter
or primary mirror segment mis-alignment will be a powerful utility during the commissioning
period. Table 1 lists the measurements needed during commissioning.
There was no identified need for high fidelity wind and optical turbulence measurements
in the telescope enclosure. This is due to existing telescopes not needing such measurements,
however there is uncertainty about whether this can scale up to an observatory the size of the
TMT. The baseline plan for the TMT SCMS and Engineering Sensors (ESEN) proposes for sonic
anemometers to be located in the enclosure vents and on the telescope structure and requires
that the communications and power necessary to support such an array of sensors is in place.
3.4. Science Analysis
There are general types of measurements that are often considered by astronomers when inter-
preting their observations, these are listed in Table 1. However a common experience is that
the scientific interpretation is greatly assisted with the availability of AO telemetry, telescope
control system and Engineering Sensor (ESEN) measurements. It should be noted that the
utility of measuring the turbulence profile is minimal because of the availability of AO telemetry
and dominance of optical aberrations in the instrument over any smaller AO related effects.
Here we present two examples of sets of observations whose analysis and interpretation is
limited by effects that can be better understood with appropriate measurements from an SCMS
in the first case and from engineering data in both cases. This is done to illustrate that the
SCMS must be considered part of a suite of sources for observatory related information that
may be needed to maximize the scientific output of the observatory.
3.4.1. Uncorrected artifacts in diffraction limited images
The quality of correction of an AO system varies with time, on the most rapid timescales this
is purely due to limitations in the wavefront sensing and correction abilities of the system. Some
AO systems introduce long lived features that mimic diffraction patterns. When bright, these
patterns are easy to identify but if two or more faint patterns below the detection limit coincide
then they may create a false detectable ’source’ in the image.
Identification of transient features in AO corrected images is a major limitation. Figure 2
shows the Milky Way Galactic Center and the G2 object that both moved and showed large
variations in brightness. Discerning between variable artifacts and the combination of real mo-
tion and brightness variations was a very difficult task.
AO telemetry is extremely useful for discerning between real transient sources and variable
artifacts. Also the number of artifacts has some dependence on seeing. Thus a combination of
SCMS seeing measurements and AO telemetry is needed.
3.4.2. 1.27s oscillation in rapid Keck spectroscopy
Telescope control systems are not perfect and can introduce image motion. Figure 3 shows
rapid tsamp=72ms optical spectroscopic observations of the Cataclysmic Variable AE Aqr
that were folded on the 33 second spin period of the magnetic white dwarf [3]. During the
analysis of the observations relatively large oscillations were found at a period of 1.27s in
both the wavelength dispersion direction (seen in variations in wavelength of static atmospheric
absorption lines) and the temporal direction (seen in variations in the flux levels). These 1.27s
Adapting to the Atmosphere Conference 2014 IOP Publishing
Journal of Physics: Conference Series 595 (2015) 012033 doi:10.1088/1742-6596/595/1/012033
4
Figure 2. The G2 object and its path toward the SgrA* SMBH at the center of the Milky
Way. Identifying the G2 object along its path was greatly complicated by the occurrence of false
positive sources created by mis-corrections from the AO system and the G2’s intrinsic variability.
variations corrupted and masked the very subtle intrinsic signals in the data. However the same
1.27s variation was seen in other objects observed during the same observing run and enquiries
with the observatory engineers identified the 1.27s period as being related to an instability or
resonance in the telescope drive system. Applying appropriate corrections to the data to cancel
the 1.27s signal allowed the signature of the white dwarf rotation to be extracted.
Figure 3. Trailed spectrograms of AE Aqr folded into 20 phase bins on 33 second white dwarf
spin period and repeated for clarity. The left image shows the continuum emission with the
pulsation amplitude rising toward the blue and the major peak occurring at phase 0.5, the
minor at phase 1. The right panel zooms in on the emission lines and S curve type signatures
can be clearly seen.
Adapting to the Atmosphere Conference 2014 IOP Publishing
Journal of Physics: Conference Series 595 (2015) 012033 doi:10.1088/1742-6596/595/1/012033
5
4. Conclusions
Clearly some form of an SCMS is a critical component for telescope operations. An important
aspect that was identified was the need for engineering data that would be used in concert with
site conditions measurements for all operations, commissioning and science analysis activities.
Engineering data would include but isn’t limited to AO telemetry, observatory engineering
sensors and control system telemetry. Interestingly, the need for optical turbulence profiles
was deemed ’interesting’ but not of high importance, for example, for astrometric measurements
of AO corrected images, instrumental distortion mapping will dominate over systematic AO
correction limitations and also there is not a strong need for turbulence profiles during operations
unless an adaptable secondary mirror is being used for ground layer AO corrections. Seeing and
wind speed and direction measurements are used for many different aspects and are thus high
priority measurements for an SCMS.
5. Acknowledgements
Many members of staff at operating observatories and active observational astronomers have
provided input to help guide the development of technical requirements for the TMT SCMS.
The TMT Project gratefully acknowledges the support of the TMT partner institutions.
They are the Association of Canadian Universities for Research in Astronomy (ACURA), the
California Institute of Technology and the University of California. This work was supported
as well by the Gordon and Betty Moore Foundation, the Canada Foundation for Innovation,
the Ontario Ministry of Research and Innovation, the National Research Council of Canada, the
Natural Sciences and Engineering Research Council of Canada, the British Columbia Knowledge
Development Fund, the Association of Universities for Research in Astronomy (AURA) and the
U.S. National Science Foundation.
References
[1] Ota´rola, A., et al., 2010, PASP,122, 470
[2] Scho¨ck, M., et al., 2009, PASP, 121, 384
[3] Skidmore, W., et al., 2003, MNRAS, 338, 1057
[4] Skidmore, W., et al., 2011, RevMexAA, 41, 70
[5] Travouillon, T., et al., 2015, this proceedings
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Journal of Physics: Conference Series 595 (2015) 012033 doi:10.1088/1742-6596/595/1/012033
6


The Thirty Meter Telescope Site Conditions Monitoring System

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The Thirty Meter Telescope Site Conditions Monitoring System

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