The Observed Surface Currents page provides an ability to display, animate, and download data
from the set of Nortek profilers that Stevens is currently deploying, including both real-time and
historical data. Some things to note about the data itself:
How to customize the data display
- These instruments can provide current directions and speeds for a range of 100 meters from the instrument,
and they are typically
placed at the end of a pier to increase the distance from the shore for which data is obtained.
Normally the data you see reflects the speed and direction of the currents. However, if a ship or other
vehicle interrupts the acoustic field, the data will be temporarily distored until the vessel has moved
out of range.
While they are called "surface" current profilers, how close they are to the
surface will vary with the tides, as they must be deep enough so that they are at least a meter
below water level at low tide, and thus will be significantly below surface at high tide.
- The data is reported every six minutes and each interval includes data from 20 locations, each one
5 meters further from the profiler than the previous one.
On the google map we show arrows for all 20 cells. The arrow will point in the direction the current
in that cell is moving and the length of the arrow is a relative indicator of speed.
Note that duration the animation the arrows are red, but when the animation is complete they will turn
white to indicate that you've reached the end.
In the table above we select 10 cells and show the distance from the profiler and the speed for that cell. The selection of which
10 to show in the able is a function of the location. Note, however, that if you download the data, all
20 cells for each six minute period will be included.
- Because this is observed data, and has no forecast component, the most recent data for any station is
within the last six minutes. You may retrieve up to 24 hours of data prior to 'right now' and you can select
an earlier date for both animation and download.
Option changes during animation
- When you enter this page, you'll see a Google map with markerfor each station (a red circle with
and exclamation point). You may select
a station either by clicking on the map icon or clicking on the silver button at the top of the page with the name of that station.
- After selecting a station, you may click on one of the duration buttons
(past 2 hours, past 4 hours...) which indicates how far back from the present moment
you would like to go. The default time period is 2 hours. You may also enter specific
Start and End date/times using the Start Date and End Date buttons below.
- Time Zone: To the left of the distance and speed table, there is a cell that shows the hour and minute
for the current reading on display, and this changes durin animation. The Time Zone control how this time
is displayed and affects the time period when data is downloaded. Local Time adjusts for DST.
- Speed determines whether the speeds are shown in knots or meters per second.
- Animation determines how quickly the page moves from one reading to the next.
There are four choices; Normal is between Fast and Medium
- There are two date/time displays to the right of Animation that will reflect the times that will be
animated or downloaded based on the time zone you've selected and the duration button you've chosen.
You may also use the Start Date and End Date buttons to set specific start and end date/times.
To use the date widget that appears you must first change the time (at the bottom)
and then click on a date.
You may change the animation speed at any time during the animation. This will take affect when you
Pause and then Continue the animation or when you start another animation. This is useful when you would
like to get to a certain point quickly and then move slowly through a time period.
Note that if you change the time zone or units during the animation it will automatically be reset to
ensure consistency. If you do this, just press Start to restart using the new options.
Using the green action buttons
- Start: To start an animation you must have selected a station. If you don't click on a duration
button the date/times in the start and end date fields will be used, and they will default to 2 hours when
you first enter the page. Start will download the data and
show red arrows that represent the direction and speed of the currents for that cell for that reading.
For each reading, the Distance and Speed tables above the map will show how many meters the cell being shown is
from the station, and the speed of that current reading. Normally, the animation will continue for the duration
you've selected and when finished the last reading will remain on view.
- Pause/Toggle: This button, to the right of the Start button, will be blank until you start an animation,
at which time it will show Pause. When you are paused (see below), it will show Toggle, to indicate that
while paused you may toggle the speed boxes next to the arrows on and off.
When you pause the animation, 20 small boxes (one for each bin) will appear next to the arrows, noting
the exact speed at that location. They will overlap at the default zoom level but zooming will
separate them. Note that at the end of the animation Toggle will continue to be shown so that you can
toggle the final values.
While paused, you may also change any of the drop-down boxes. Changing the Animation speed will allow
you to continue with those changed. Changing anything else will require that the animation be restarted,
either by pressing Reset during the animation or pressing Start when it has finished.
- Continue: Once you've started an animation, the Start button will show Continue rather than
start. This both makes it clear that you're in an animation, but it also indicates that this
is the way to resume a paused animation.
press Start again.
- Reset: If, during the animation you would like to cancel it, you can press Reset (either during
the animation or when paused) to clear the animation. This does not change your selection of station
and duration, but erase the data.