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Designing Embedded Hardware

Computers for Albatrosses

by John Catsoulis, author of Designing Embedded Hardware
12/03/2002

In my work as a computer-design engineer, I create new machines for novel applications. When an off-the-shelf computer system simply won't do, I nut out a solution, marrying unique hardware with tightly coupled software. As you might imagine, projects that require unique computers are often unconventional. Sometimes they involve controlling unusual systems. Other times they involve providing high-performance processing power in a souped-up machine that's not weighed down with a bloated operating system. More often than not, the projects involve gathering and storing data. Some of those applications require rapid data acquisition. If they do not, a simple 8-bit processor normally does the job.

The Project: Designing a Datalogger to Track Albatrosses

It was in 1997 that I received a phone call from David Nicholls. David is an ecobiologist, and he has been studying the albatrosses of the Southern Ocean for several decades. He pioneered the use of satellite tracking for these birds, and has been a driving force behind the advancement of electronics in wildlife monitoring.

Albatrosses are magnificent seabirds that soar just above the ocean waves, with their enormous slender wings bent in shallow arcs. Their wing spans can be up to 12 feet, yet they are very light. Albatrosses spend the entire year flying, only coming to land during breeding season. Non-breeding albatrosses can spend as much as five to ten years at sea, never touching land. They circumnavigate the world many times over. It is not unusual for a bird to leave its nesting ground on a remote island off New Zealand, and, within a week, to have soared across the Pacific and reached the southern tip of South America. They regularly fly south to Antarctica and travel huge distances around its frozen coastline. One bird was tracked flying 3,000 kilometers from Australia due south to Antarctica, then it flew 3,000 kilometers along the Antarctic coast. At this point, it turned around and followed the same path 6,000 kilometers back to home.

As David put it, "For me, an albatross is speed, elegance, precision, and self-sufficiency in a beautiful and sometimes dangerous, often harsh, environment. The bird is a survivor. It flies 1,900 kilometers (1,100 miles) per day, with pinpoint navigation, and returns to its nest repeatedly over its 50-year lifespan. An albatross flies at speeds of 135 kilometers per hour or more, all without a feather out of place. They are precision at wave-top height, and at sometimes thousands of miles away from any support."

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What these birds do and how they live has been a great mystery, and there are ongoing research programs in place to investigate their biology and ecology.

So as I said, I received a phone call from David. He introduced himself and said he wanted a "simple" datalogger designed. At that point in my career, most of my design work had been with 32-bit and 64-bit processors, using high-speed systems. If I had need of an 8-bit processor, I'd just use a Motorola 68HC11. It was simple and easy to throw together a system. You could design the hardware before lunch, and then spend the afternoon cutting the code. It's not that the HC11 was necessarily the best 8-bit controller around, simply that it was familiar. It was rare that an application presented itself that did not allow a HC11 to be hammered into a solution, that is until that phone call in 1997.

The Problem: Creating a Miniature Datalogger

When David said he needed a datalogger, immediately visions of HC11-based computers, with separate RAM and ROM, danced in my head. He said that he wanted it small. No problem, I thought. HC11 computers are small, ranging in size from a playing card to a paperback novel, depending on the application. "I want to put it on a bird," he said. "You want to what?" I replied. He then went on to tell me about albatrosses, and how he wanted the datalogger to operate for a year or more on a small battery. And since it can be up to 10 years or more until recovery, the datalogger had to retain data for that long. And by small, he meant the size of your little finger. Immediately, the visions of HC11s vanished. There was no way a HC11 system was going to be suitable.

Prior albatross research had used satellite tracking systems, known as PTTs (Platform Transmitter Terminals). Some of the weather satellites operated by National Oceanic and Atmospheric Administration (NOAA) also carry a subsystem known as ARGOS. The NOAA satellites, of the advanced TIROS-N class, are polar-orbiting spacecraft flying at relatively low altitude. The ARGOS system they carry is used in wildlife research to gather location data and report it back to a command center (located in France). Animals under study carry a PTT (typically 3-inches by 2-inches in size) that transmits an identifier code. When the satellite passes overhead, it records the code and from the satellite's position, a fix on the animal is obtained. However, a satellite pass over a given location will only occur once every six hours or so, and only very limited data uplink capability is available. Most PTTs will only provide location information, and those that record other data are only capable of uploading short statistical summaries.

For detailed behavioral profiles, PTTs simply won't cut it. PTTs leave many questions unanswered. David wanted a system that went beyond simply providing six hourly location fixes. A recoverable datalogger recording detailed sensor information was required to solve mysteries about albatross behavior.

The Solution: Using a PIC Processor

And so the hunt began for a small, ultra low, power processor suitable for such a datalogger. The hunt ended with the PIC processor, and the resulting computer system was just 32 millimeters by 16 millimeters, with 2MB of serial flash, integrated data compression, advanced power management, configurable sensitivity, control of sensors, and a graphical user interface for a host computer.

These dataloggers have now been in use for several years and have revealed considerable new insight into albatross ecology. The proprietary data-compression system I developed is able to condense up to 40MB of data into the onboard 2MB of memory. Since the memory is based on Flash technology, the datalogger will retain recorded data for up to 20 years, without power. Thus, even if the battery fails during a long deployment, the information is not lost.

The tiny datalogger weighs one-fifth of an ounce and is attached to the birdís leg. The attachment is designed and fitted with great care to ensure that the bird is not harmed or adversely affected in any way. An onboard light sensor is used to record sunlight levels that the bird experiences on its journey, and a temperature sensor measures daytime minima and maxima, as well as minor fluctuations due to behavioral influences. These two sensors can provide a wealth of information about the albatross.

The Result: Learning More About Albatrosses

By comparing the recorded sunrises and sunsets with the reference clock aboard the datalogger, and by looking at the duration of twilight, we can compute latitude and longitude. In this way, the simple recording of light levels is used to track an albatrossís journey as it circumnavigates the world. For example, if the datalogger is configured and deployed in New Zealand (longitude 170 degrees east), and the albatross flies eastward to Tierra del Fuego (longitude 70 degrees west) on the southernmost tip of South America (a change in longitude of 120 degrees), then sunrise and sunset will happen eight hours earlier, according to the onboard clock. The progressive shift in the times of sunrise and sunset not only provides positioning information, but also rates of migration.

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The actual algorithm used to compute the progress is a little more complicated than I've alluded to here, since the terminator (the boundary between night and day) does not run north-south, but is inclined at an angle. Therefore, changes in latitude can provide a degree of error in the calculation of longitude. However, a change in latitude also brings variation in the length of twilight. The further south you go, and the closer to the pole you get, the longer the twilight becomes. This information combined with temperature data, cross-referenced to satellite sea-surface temperature, is used to reduce the overall error.

You may wonder why GPS (Global Positioning System) isn't used to determine location. GPS would provide far more accurate position determination, but GPS modules tend to be bulky (in comparison to the datalogger) and are incredibly power hungry. The batteries required by the GPS unit for an extended deployment would simply place too much of a burden on the albatross. So the datalogger provides the best balance between weight and data-gathering requirements.

The recorded light profiles also give information about what the albatross does. You can tell whether the bird was flying with feet tucked up in the feathers, flying with feet hanging down, or resting on the water, as each activity has a unique light profile associated with it. You can also see the phases of the moon leaving their trace on the nighttime light levels, as well as which days were cloudy and which were sunny. It even detects when the albatross stumbles across a lonely, and brightly lit, squid boat during the night. One simple sensor can tell you a lot.

The temperature sensor also provides behavioral data. While the sea and air temperatures may be just above freezing, under the feathers can be quite warm (104 degrees Fahrenheit, or 40 degrees Celsius). Thus, if the temperature sensor records temperatures close to freezing, the bird has its feet down exposing the datalogger (and therefore the temperature sensor) to the outside environment. However, if the sensor records 104 degrees, then the feet (and the datalogger) are safely tucked under the feathers, keeping warm.

You can go even further in determining behavior from temperature data. When the albatross is resting on the sea surface, its webbed feet are used to paddle around, and so the sensor records the ocean temperature. When the bird takes off, evaporative cooling from the wind causes the recorded temperature to drop below freezing, as the sensor is exposed to the prevailing winds (and there is a constant and severe wind in the Southern Ocean). However, if the albatross takes off and immediately tucks its feet up, then the temperature does not show evaporative cooling. Instead, it rapidly climbs as the sensor is warmed under the feathers. Interestingly, different albatrosses have different preferences for take-off. Some birds will consistently leave their feet hanging down (presumably to dry them off), while others will immediately tuck their feet into the feathers as soon as they leave the water. The datalogger and its sensors provide an insight into the quirky personalities of seabirds, flying alone in a vast emptiness.

The sensors have shown that albatrosses fly considerably faster than was previously thought. Satellite-based PTT studies provide positional information once every six hours, and it was assumed that the albatrosses flew at a consistent rate of approximately 20 mph during this period. From the positional information and the calculated average flight speed, the datalogger has shown that this is an inaccurate assumption. Rather than flying for the six-hour period, the albatross spends considerable time simply resting on the ocean, and when it does fly, it travels at speeds of between 60 and 90 mph.

Conclusion

The datalogger has proven a reliable tool in albatross study. Beyond that, it has provided a bridge between two worlds, linking hardware engineering to the remote, desolate, and beautiful Southern Ocean. It has given me the opportunity to be involved in a field that is far removed from my normal work. It has allowed me to experience the realms of the albatross, a stark contrast to the day-to-day complexities of computer hardware. And that's the neat thing about this business. You never know quite where the next project is going to take you.

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