DSS Minimum Observing Condition (MOC)

  • Description

The minimum observing condition (MOC) is used to evaluate if a currently scheduled session should be executed or if the weather conditions have deteriorated enough that a backup session should be scheduled instead. There are only two metrics that are used to determine the MOC: the observing efficiency (\eta_{obs}) and the tracking efficiency (\eta_{tr}). The MOC for each of these metrics must be met to execute the scheduled session. The table below describes these metrics.

Observing Efficiency (\eta_{obs}) Tracking Efficiency (\eta_{tr})
obsEff.jpg TrackEff.jpg
The observing efficiency versus frequency. The observing efficiency is defined as the ratio of the integration time needed to make a transit observation in the best weather to the time needed to reach the same sensitivity given the actual weather conditions and hour angle. An observing efficiency of 0.5 means that twice as much integration time will be required to achieve the same signal-to-noise ratio under the best weather conditions based on historical data. The points correspond to scheduled sessions from a DSS simulation. The blue crosses are individual scheduled sessions while the red circles are weighted averages of these data. The solid curve is the minimum observing efficiency and is based on the lower envelope of the data. The tracking efficiency versus frequency. The tracking efficiency is the component of the observing efficiency that includes tracking errors due imperfections in the pointing model plus tracking errors from wind. The curves are the tracking efficiencies for different wind speeds and are truncated when the rms flux errors reach 10%, corresponding to 20% of the GBT's full-width half-maximum beam size. The solid and dashed curve correspond to the night and day performance, respectively, and reflect the better pointing conditions at night.
MOC for \eta_{obs} MOC for \eta_{tr}
\eta_{obs} > \eta_{min} - 0.1 Tracking errors that result in rms flux errors \le 10\%. When this condition holds the tracking error limit \ell_{tr} = 1; otherwise it is zero.

  • Implementation

Apply the MOC only for sessions that have already started or will start within 6 hours from the current time (now). On the schedule page have the blinking icon when the MOC is not met. Two sets of weather data should be used:

  1. The best weather forecast and WS2 wind data for "now". (PaulMarganian: WS2 == raw Weather Station 2 wind speeds)
  2. The best weather forecast, including corrected wind data, for the start of the session. (PaulMarganian: corrected wind data == forecasted wind data from CLEO that has been corrected to scale with the WS2 data)

Calculate the MOC for both (1) and (2). But only apply the MOC for (1); that is, the session will only blink if the MOC using (1) is not met.

The following information should be given:

  1. MOC for (1) and (2) if the session is within 6 hours of "now".
  2. Information about MOC (above).
  3. Information about the weather (CLEO forecasts, Charleston weather page).
  4. Scoring page.


  • Dana's Notes

The original concept behind the minimum observing condition (MOC) was
to determine 30-60 minutes before a session was scheduled to begin to
check if the weather was still good enough for this session.
Quantitatively, good enough---the MOC---was defined to be:

a. Based on the most recent forecast and WS2 wind speed data is the
following true:

observing efficiency > minimum observing efficiency - 1

where the minimum observing efficiency is the solid curve in Figure 9 in
DSPN5 (or the solid curve in the figures on the T-shirt).

b. Based on the WS2 wind speed data is the following true:

tracking error limit = 1

If either of these conditions is not true then we try to schedule a
backup session or sessions.

Some Questions:

1. How do we describe the MOC to observers or more generally how do we
inform the observer about the current conditions once their session

We could point them to the DSPN5 for details.  But maybe we need a
short description of this that is somewhere in detail between the memo
and what we have in the glossary.
Also, it might be good to have all the related info about performance
in one place.  For example, they might want to check out Ron's
forecast page, the scoring page, and the MOC.

2. When to apply the MOC on the scheduler?

The MOC was originally for NRAO to determine if a session should run
before it was scheduled or not.  Once a session starts it is up to the
observer to determine if they want to continue or not.  While it might
be useful for the observer to know if the MOC becomes false during
their run they do not see the scheduler and having the MOC visible on
the scheduler will probably confuse the operator into thinking that
*they* have to do something. Therefore, I would not apply the MOC on
the scheduler once a session starts.

Also, how far into the future should we apply the MOC?  Based on the
structure function analysis we determined that 6 hours is the time at
which weather changes.  So I would apply it 6 hours into the future
which I think is what we are doing now.  This will give the operator a
heads up for future sessions.

3. At what time or times during the session do we calculate the MOC?

Do we use the start time of a session as when to calculate the MOC or
do we use some weighted average over the duration of the session?  I
would only use the start time since if this time is good then it
should be up to the observer as whether to continue or not.

Consider five sessions: A - E.

 |     A     |       B          |  C   |      D     |     E       |
                         ^                     ^
                         |                     |                            |                     |
                        Now                Now + 6 hr

Since session B is already running I would not apply the MOC on the
scheduler.  I would apply the MOC to sessions C and D using the start
time but not to session E.

  • Karen's Notes from DSS Meeting

    * Need to better describe them
    * When to apply:
          o Before a session - how far in advance? Using what time (start time, middle)?
          o During a session - notify?

Answer: apply for everything from now through the next 6 hours; 
On the schedule page have the blinking icon when min obs conditions not met. 
For all TP within the upcoming 6 hours period, give info of: current and 
predicted winds, MOC, anything else Dana feels appropriate plus a link to at 
least the Charleston pages and also Ron's pages. or maybe embed the Chas. 
pages within the link. Also need documentation on what this is (
e.g. in glossary and user's tutorial).

Side issue: need to color code or otherwise contextualize the tabs.

-- DanaBalser - 03 Jul 2008
Topic revision: r4 - 2009-04-27, DanaBalser
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