Real time experimental moorings:An OASIS in Monterey Bay, California
OASIS :Ocean Acquisition System for Interdisciplinary Science
Francisco P. Chavez,
and Gary Thurmond
Updated by Mark D."Zorba" Pickerill
Recent OASIS can being readied for deployment
The importance of time series in oceanographic research
is clear. Time series measurements of physical and
meteorological properties, currently taken throughout the globe,
have allowed investigators to resolve the important scales of
oceanic and atmospheric variability. With a few exceptions the
current time series are primarily physical in nature (i.e.,
temperature). Biological and chemical oceanographers are now
looking to continuous observations of biological and chemical
properties so they can also determine the spectrum of variability
in these fields and when taken concurrently with the physical and
meteorological observations determine the relation to climate and
ocean variability. Spatial coverage will ultimately come from
observations made from space, but high-frequency temporal and
added vertical coverage will need to come from moorings and
drifters with arrays of in-situ sensors. The paucity of
biological and chemical time series has been due, in part, to the
lack of this type of instrumentation, however, increased effort
has recently been placed on the development of chemical and bio-
optical instrumentation for the collection of these time series.
Realizing that advances in ocean sciences are limited by the lack
of instrumentation and systems capable of collecting these time
series, the Monterey Bay Aquarium Research Institute (MBARI) has
established a vigorous developmental program geared at making
these observations possible.
One of the goals of the program was to develop a new set
of control electronics and software that would allow for the
collection, storage, and telemetry of data from any of a wide
range of scientific instrumentation. The controller, OASIS
(Ocean Acquisition System for Interdisciplinary Science), and its
deployment in moored and drifting systems, is the focus of the
present contribution. Additional impetus for designing such a
system were the increased need for real-time environmental
information, the need to easily add new instrumentation as it
came forward and the need to test new instrumentation with
rapidity and in an environment that was well documented with
respect to other properties. The ability to add devices is key
when new instrumentation is being developed at a rapid rate.
Testing of new instrumentation is best carried out on an easily
accessible platform where a basic set of observations are
routinely taken (temperature, salinity, wind speed and direction,
etc.) so that data from the new instrumentation can be readily
analyzed and interpreted. The advantages of two-way real-time
telemetry are several-fold. It allows for quality control of
data so as not to lose long, expensive mooring deployments. The
data is immediately available for analysis, assimilation into
models, and calibration of satellite sensors. The information
provided in real-time by the system can be of tactical use for
shipboard experiments, especially those geared at specific
events. Finally, instruments can be accessed remotely so that
sampling frequency can be modified according to needs or trouble-
shooting performed without retrieval.
The initial scientific and technical objectives were:
1) Establish a a platform for the deployment of a set of
unattended sensors and samplers.
2) Design a general purpose controller that collects data from
scientific instrumentation via multiple interfaces and then
telemeters the information real-time.
3) Make continuous observations of physical, chemical and
biological properties in Monterey Bay and the associated coastal
central California ecosystem so as to describe time-varying
aspects with increased resolution and over long periods of time.
4) Contribute to the improvement of mooring and unattended sensor
technology, with emphasis on biological and chemical properties.
5) Provide groundtruthing for properties sensed from space.
The engineering objective of the mooring project was to
develop a new set of control electronics and softwarethat would
allow for the collection, storage, and telemetry of data from any
of a wide range of scientific instrumentation. Considering the
rapid rate of instrument development it was important to design a
system capable of multiple interfaces. A general-purpose
controller was designed so that it could interface to scientific
instrumentation via any anticipated method, including:
- RS 232 (110 to 38400 baud);
- Analog voltage;
- Digital logic (5 volt TTL or CMOS);
- Frequency measurements, including pulse modulation;
- Power control (turn device on/off);
The controller, centered around the Intel 87C196 chip
acquires data from the configured sensors, stores the
data as required, and telemeters the data back to shore via
packet radio. The controller is easily extensible and
programmable. By extensible it is meant that new devices can be
easily added. It is programmable, allowing the user to change
parameters such as sample rate, interface parameters and
telemetry parameters from shore. The controller has also proven
useful for other applications and for acquisition of data from
other platforms such as drifters.
The design of the OASIS board considered, in
addition to extensibility, low power and reliability. At the
current operating speed of 9.830 MHz (the CPU is capable of
operating from 3.5-16 MHz) the board consumes 75 mAh/day @ 12V,
which is small relative to consumption by the instrumentation.
On the present moorings all power, provided by a lead
acid battery (9-18V) recharged by an array of solar panels, is
shunted through the controller.
The controller schedules a real time clock to put it to
sleep and wake it up for its next task. There are three UART's
on the board. One is on the 87C196 chip and serves either the
terminal or the packet radio; the other two are external and
serve the instrumentation. There are sixteen (16)
latching relays for the two external UART's allowing for
connection to the same number of serial devices. The original
design encorporated only 8 relays, but it was found that the
M1 site exceeded eight instruments, necessitating a second
controller addition, but with the 1996 deployment one controller
now has the capability of handling sixteen (16). The latching relays
are used for reliability so that the system is completely
isolated from the environment and/or sensors. Parallel I/O and
bus expansion are also available on the board. Analog
conditioning and the power switching circuitry are on a small
"daughter" board. Memory on the controller, external to the CPU,
is divided into three categories. A socketed 32K EPROM device
contains the program code. So-called data or scratch RAM and
logging RAM are used for program elements and data storage
respectively. Current allocations are 24K and 1 MB. The use of
small IDE hard hard drives for larger data storage applications
is also been added in 1996. In the present (Monterey Bay)
application data storage is only an issue if the telemetry link
is down as all data are telemetered to shore every hour.
However, for remote applications, such as MBARI's participation
in Eq-Pac, all data can be stored on disk, greatly enhancing long
term data aquisition capability.
There are two major software efforts for the OASIS
project, on the mooring and on shore. On the mooring the
programs running on the 87C196 are written in C. The core of the
code is a multitasking scheduler that controls wake up and
interfaces with a series of drivers. There are drivers for the
user interface, packet radio and each instrument. In this sense
the programming is modular, so that if a new instrument is to be
added, a new driver is developed and added to a table. In
addition each driver has a generic set of parameters. There are
a set of default parameters for each driver that are called from
a table when the system boots or resets and these can be modified
through the user interface either directly or over the packet
radio link. The current C code occupies 25K of the available 32K
of EPROM space. A significant aspect of the software is that it
allows users to directly connect to serial devices via the user
A typical set of operations is as follows. The clock
wakes up the controller at a predetermined time. The scheduler
starts the drivers that are on its list and then waits until they
return with a task completed message. Once all tasks are
completed the scheduler requests that the clock put it to sleep
and wake it up for its next schedule of tasks. One particular
task involves communication between a computer on shore and the
controller. Currently the controller listens for the remote
connection for twenty seconds once every ten minutes (under
software control). Once communication is established the on
shore computer requests all data since the previous request for
data. The data from the instruments are uuencoded by the
controller software to reduce the size of the files and therefore
reduce storage and radio transmission time.
The collection of data from shore is automated by
software running on a Hewlett-Packard workstation. The software
is combination of C code, UNIX shell scripts and UNIX cron jobs.
A cron job is initiated once an hour on the hour to request data,
through shell scripts, from n (maximum number has been four
when a drifter has been deployed) controllers deployed in Monterey
Bay. The shell scripts request data from the controllers and then
initiate a series of C programs that extract and decode the data files
These programs apply calibrations and append the data to daily
files ASCII in instrument-specific directories. Each file has a
header that describes the contents of the file. Once daily,
during off hours, the data files are concatenated into files that
span the entire deployment period.
Instruments and their interface
The majority of instruments are interfaced via RS-232 and a few
are analog. The thermistor chain, wind and compass are frequency
measurements made by ATLAS but similar capability exists on OASIS
and these measurements could be subsumed if desired. The most
common serial interface consists of power, receive, transmit and
ground. Because each instrument has its own particular
attributes each interface is different and some require more
software than others.
Instruments such as RDI's acoustic doppler
current profiler (ADCP) and Biospherical's PRR-600
spectroradiometers broadcast data while others like the Seabird
Seacat can provide data upon request. The interface
characteristics of some of the core instruments are described in
the next few paragraphs.
The ATLAS, ADCP, Seacat and the nitrate
analyzer are stand-alone systems. ATLAS collects and stores
meteorological and ocean temperature information once every ten
minutes. Software in ATLAS has been modified from their standard
use in the equatorial Pacific by PMEL so that the OASIS
controller can access the ten minute data. Once every ten
minutes, but not during the time ATLAS is collecting data, a
control T is sent from OASIS to ATLAS and ATLAS responds by
providing its last set of measurements.
The ADCP is programmed
to take a measurement once every 15 minutes. Once the data
acquisition and processing is finished the ADCP sends the data
out through its serial line and stores it internally. OASIS
listens for the ADCP data once every 15 minutes and collects it.
The Seacat is programmed to take a measurement every ten minutes
and OASIS wakes it up and requests the last sample. A similar
dialog exists between OASIS and the nitrate analyzer. The
analyzer, run by a Tatletale IV, takes a measurement every five
minutes and stores it. OASIS wakes it up once every thirty
minutes and gets the data since the last request.
There are also
several instruments that depend on OASIS for data collection and
these include the GPS, Biospherical spectroradiometers and LICOR
carbon dioxide (CO2) analyzers and photosynthetically active
radiation (PAR) sensors.
The GPS receiver is turned on once
every thirty minutes and three minutes of data are then collected
and averaged by OASIS. For the PRR-600 spectroradiometers, OASIS
turns on the power and listens for the data. There are three
PRRs daisy-chained on one line that has the transmit and receive
cables shorted so that all instruments can hear each other. Each
instrument contains two CPUs (one for downwelling irradiance and
one for upwelling radiance) and each CPU has a unique identifier.
One scan of data from each CPU is transmitted sequentially and
OASIS averages n scans (under software control) so that a truly
synchronous measurement of irradiance and radiance at several
levels can be accomplished.
For the MER series of
spectroradiometers the units are turned on and programmed by
OASIS on every sample, and the data collected after the
instrument averages on board. In the current configuration the
analog data from two near-surface Satlantic OCR-100
spectroradiometer are digitized by a MER 1010 along with data
from an above water irradiance sensor.
The CO2 analyzer is
turned on every hour by OASIS and given instructions as to what
data to send. After allowing three minutes for the embedded
thermoelectric cooler to reach equilibrium it requests a sample.
Once every four hours a string sent to the instrument instructs
it to actuate a valve so that both cells sample air. In addition
OASIS turns on/off a small pump in an equilibrator that feeds
ocean-derived gas to the analyzer. The PAR sensors are current
generators, so after conversion from current to voltage on the
daughter board the signal is digitized by OASIS.
The telemetry system used by the OASIS project is based
on packet radios popularized by the amateur ham radio operators.
On the mooring there is a miniature 1200 baud AX.25 terminal node
controller (TNC) and a R-net 2 watt telemetry module. On shore
and at a repeater site on Mount Toro rack-mounted systems with
the same characteristics are deployed. Transmissions occur on
the 460 MHz band and the present effective baud rate through the
repeater is 2400 baud. At the current data collection rates the
radio frequency is used on the order of 25% of the time so that
throughput is not limiting.
There are currently two
moorings deployed in and around Monterey Bay, California
Since the offshore site is not within line of sight of the
shore laboratory a repeater was deployed at 1000m elevation on
Mount Toro. This increases the range of the telemetry system to
on the order of 140 km from shore.
Mooring and drifter hardware.
The OASIS controller has been deployed on three different
sets of platforms. In the moored configuration, ATLAS and
PROTEUS moorings were modified to allow for deployment of OASIS,
a solar panel array, an elevator assembly for near surface
instruments and cages were added subsurface at 10 and 20 m for
additional instruments. The primary difference
between ATLAS and PROTEUS is that the latter has a four leg tower
and bridle (ATLAS has three) to accommodate deployment of an
ADCP. Current deployments are an ATLAS-like mooring at the M2
site and a PROTEUS-like mooring at M1. Strategically the M1 site
is considered the development site and M2 the site were "mature"
technology is deployed. However, because of proximity to shore
most of the instrumentation is deployed at site M1. This
requires more power at M1 and the solar power array there
consists of eight 10 watt panels while at M2 there is a three
panel array. The solar energy is used to charge a 90 amp-hour
lead acid battery capable of operating the system for two weeks
without recharging. The battery is connected directly to OASIS
and it (OASIS) provides power to all the devices. One exception is the
marker light that receives power directly from the battery.
Additional outlets are available on the battery.
been built on both moorings to service the near-surface
instruments. Service includes replacement of devices and removal
of biological growth. Goose neck barnacles of the genus Lepas
are a particularly severe problem that require regular attention.
Stainless steel cages are deployed at 10 and 20 m for instruments
such as spectroradiometers, additional CTD sensors, nitrate
analyzers, acoustic modem hydrophones, etc.
electronics, including the packet-radio hardware and GPS
receiver, is housed in a 8 1/2" OD PVC tube 24" long. An PVC
face plate has been machined to hold three split connectors (6
each), dorn bushings for antenna coax, and a ball bearing feed
through to allow pressurization of the can.
The OASIS can has
also been deployed successfully on a drifter. In this
configuration the can is bolted on to a ionofoam doughnut with
about 100 lb. floatation. A stainless steel bridle allows for
attachment of a stainless steel cage and a holey sock drogue
similar to those used in WOCE drifters. In the drifter mode
power is provided by D-cells. Ten (10) D-cells provide enough
power for a GPS position every 15 minutes and a radio
transmission every hour for 14 days. Up to 20 D-cells can be
accommodated in the present can design.
Results to date
ATLAS moorings were first deployed at sites M1 and M2 in
the waters adjacent to Monterey Bay in August 1989. The initial
deployments were used to determine if these types of moorings
could be maintained in a coastal environment, with heavy fishing
pressure, for long periods of time. The sites were selected
primarily for scientific reasons but after discussion with the
local fishermen. The moorings have survived well to date and
vandalism has not been an issue.
In 1992 the two moorings were
re-deployed with novel sets of control electronics capable of
assimilating data from multiple instruments and telemetering it
real time via packet-radio and/or satellite. Data from a
thermistor chain, meteorological instrumentation, CTD's with
fluorometers and transmissometers, SeaWiFS-compatible
spectroradiometers, an acoustic Doppler current profiler, a pCO2
sensor, nitrate analyzers, PAR sensors and diagnostic data
(battery voltage, can pressure, etc.) are currently being
assimilated and processed.
The reliability of OASIS has exceeded
expectations. The OASIS data acquisition system has only
experienced one period of down time in two years of operation due
to the OASIS hardware and software. The problem was with a
hardware component being underspecified and was easily corrected.
Failure of the peripheral devices (instruments and telemetry) has
far exceeded that of the controller.
A number of our original program objectives were met with
the initial OASIS deployment:
- Establish a platform for deployment of unattended
- Design and construct a general-purpose
- Make continuous physical, chemical and biological
observations in Monterey Bay so as to describe their
- Characterize a variety of optical instruments in remote
deployments. Real-time data is being collected at the
highest rates ever achieved for a long-term ocean mooring
system (Table 1) and many of these data are from
instruments that have not previously been reported in
real-time. OASIS, with its novel design, is one of the
few mooring systems in the world where new instruments
can be added with relative ease and their data quality-
controlled in real-time. OASIS electronics have also been
successfully deployed on a WOCE-like drifter with several
instruments, including a Seacat and a nitrate analyzer.
The collection of biological time series concurrently
with physical measurements has allowed for characterization of
the coastal central California environment with resolution that
had not been possible before. A notable result is the high but
coherent variability in phytoplankton, the small microscopic
plants that are the base of the ocean's food web. The comparison
of data from a surface fluorometer with bi-weekly shipboard
observations at the M1 site shows that many of the
bloom to bust cycles of plants in this environment are missed by
sampling at the frequencies that commonly possible with shipboard
efforts. This is particularly true for coastal environments and
the present observations are an example of the need for
continuous observations of ocean properties.
Diagrams of mooring M1 and M2:
Click on the images below for an enlarged view.
MBARI Home Page
Download OASIS schematics
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Last Updated: 02 June, 2003