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Experience has suggested the following steps for configuring ALIS for
- 1. Defining a scientific rationale:
- This is of course the first
and most important task. Naturally it is almost impossible to
predict the outcome of any observations. Nevertheless, well planned
measurements with a clear view of what needs to be done tend to
yield better results than ``ad hoc'' operations.
- 2. Selecting stations:
- Normally it is best to use as many
stations as possible, but there might be observation schemes that
require only a subset of the stations. It is also important to plan
what changes to the rationale are necessary in case
some stations cannot take part in the observation (for example due to clouds
or technical problems).
- 3. Selecting imager viewing directions:
- This can be either the
standard preset viewing-directions (Figure 3.11 and
Table 3.6) or specially calculated viewing directions for a
particular measurement. It is advisable to prepare a strategy for
possible changes if the observed phenomena moves outside of
the field-of-view. In most cases it is best to avoid changes of the
viewing directions during a measurement. ``Chasing the aurora''
usually results in poor data. Another concern is to make sure that
the selected positions are geometrically calibrated against the star
background (Section 4.3).
- 4. Selecting filters:
- Filter selection usually follows directly
from the scientific rationale. However all filters are not
available at all stations (see Tables 3.4
and 3.5). Filter change time increases with
the distance between the filters on the filter-wheel (nominally
1-2 s). It might also be necessary to obtain background intensities
by exposing images with background filters.
- 5. Selecting integration times:
- The minimum integration time is
defined by the shortest exposure resulting in an acceptable
As the spectral sensitivity varies for the imager, there is normally
a need for longer exposures for shorter wavelengths. Maximum
exposure is defined by the longest exposure without saturating the
CCD, or, more frequently, by requirements set by the desired
temporal resolution. The risk of saturating the CCD must be
considered at high binning factors as the sensitivity increases with
the binning factors (Figure 3.4). Occasional saturated
images pose no threat to the CCD, but yield unusable data.
Finding an optimal integration time has proven to require large
amounts of experience from earlier measurements. (see also
- 6. Selecting temporal resolution:
- The temporal resolution is
currently limited to one image per 30-60 s at maximum resolution,
and is generally never better than 30 images per minute at higher
binning factors. These figures vary somewhat between the imagers.
Also times for filter changes must be considered.
- 7. Selecting spatial resolution and sensitivity:
- This is
generally a compromise between temporal resolution, sensitivity,
framerate and disk-space. Note that increasing the temporal
resolution by binning might lead to saturation problems due to the
increase in sensitivity.
- 8. Deciding on data storage strategies:
- As the disk space at
the stations is limited, it is advisable to estimate the amount of
data produced and decide what data should be kept, when to retrieve
the data and if deleting presumed unusable images should be
- 9. Coordination with other instruments:
- Such as EISCAT
measurements, satellite passes, rocket launches etc. This involves
many considerations (for example when does a satellite pass occur? Should
ALIS image along the foot-point of the satellite pass?). It is also
essential to establish communication with the control centres of
- 10. Selection of a suitable operational mode for the
- Available modes are: automatic, semiautomatic or
manual, see Section 5.1.1. In order to increase the number of
observations of a particular phenomenon it would be desirable to
have more automatic runs, however, experiences indicate that at the
present, the best results emerge from manned semiautomatic runs.
- 11. Defining and testing the required configuration of ALIS:
- No usable bug-free program exists. Therefore everything should be
tested as thoroughly as possible before running the actual
observation. It is also important to start up all systems in ALIS
well in advance. The imagers need to be thermally stable and
defrosting of the domes as well as booting subsystems at the
stations might also take some time. (Estimate at least 1-2 days for
testing a new measurement scheme, and 2-4 hours to start up ALIS.)
It is also advisable to perform some rudimentary last checkout
procedures about one hour prior to starting the measurements.
- 12. Waiting for the right conditions:
- This might be a long
wait. In this phase, it is advisable to take images at all stations
at regular intervals to check weather conditions and system
performance. It is also a good practice to be prepared for many
different kinds of observations. For example, if conditions for
observing HF-pump enhanced airglow are not right, there might be an
excellent auroral event instead.
- 13. Run the observation:
- During measurements many unexpected
things can happen, so it is good to be well-prepared with
alternatives. Two to three people in the
control centre are the ideal for most measurements: one who takes
care of technical problems and runs the system, one who concentrates
on taking scientific decisions and possibly one who coordinates
with other instruments. Taking good notes is essential, as analysis
might not occur until months later.
- 14. Retrieve the raw-data from the stations:
- It is
time-consuming to retrieve raw-data from the stations. All six
stations can be visited in less than a week, but this requires a lot
of driving. Usually the disks are brought back only during scheduled
maintenance trips to the stations, or as the disks become full. If
exceptionally interesting data have been recorded, it might still be
desirable to retrieve it as quickly as possible.
- 15. Analysing and publishing the results:
- First one needs to
select data, then this data-set must be preprocessed and calibrated
before the actual analysis and publication phase starts. These
final steps rely on good record-keeping in the previous steps.
The modes for controlling ALIS are summarised below:
Modes of operation
- Manual control:
- By sending commands directly to ALIS, a user
is able to control observations interactively. This mode of
operation is most frequently used for checking observing conditions
(cloudiness, etc.), for troubleshooting and for maintenance.
- Semiautomatic operation:
- In this mode a user controls
ALIS by running observation control programs (usually these are
shell-scripts at the stations) that are uploaded, prepared and
tested in advance. This is the normal operating mode.
- Automatic operation:
- In this mode, an observation control
program is loaded and run automatically at a predefined time.
This mode can easily be switched to semi-automatic mode if the
user wishes to change anything. Exceptions can be reported using
a paging system if the control centre is unmanned. Due to the
vast amounts of data produced, automatic measurements are uncommon.
Many exceptions can be properly acted upon automatically, while others
require manual interaction. These exceptions trigger alarms, which
are displayed at ALIS-CC and at all user interfaces. If user
interface is active, an automatic paging system will also alert the
operator on duty. Typically, a pager call occurs for A-Alarms or
fatal alarms, (see below) but the paging system can be
configured to alert a user when an interesting measurement
situation is emerging, etc. ALIS exceptions are classified in three alarm
Alarms and other exceptions
- Fatal alarms:
- Fire, trespass or other severe conditions
threatening the hardware.
- Conditions causing the imaging to stop at one or
several stations (power failures, filter-wheel problems,
unrecoverable run-time errors, etc.).
- Other conditions affecting the quality of
observations (timing problems, communication problems, over- or
under-exposed images, etc.).
Up: Controlling ALIS
Previous: Controlling ALIS
copyright Urban Brändström