Lessons Learned – by Pat Carson
Is My RADAR Killing Me?
The short answer is, of course not. According to the World Health Organization, to produce health defects, exposure would need to be 1000 watts per square meter or more and marine RADARS on pleasure boats do not reach more than a few watts per square meter. You would also have to stand directly in front of the very narrow beam for a significant amount of time and that is impossible while it is rotating.
In high school we learned that there are two kinds of radiation, ionizing and non-ionizing. Ionizing radiation is a type of radiation that has enough energy to remove tightly bound electrons from atoms, thus creating ions. Examples of ionizing radiation include X-rays and gamma rays which will change a cell’s biological structure because they have enough energy to remove an electron (negative particle) from an atom or molecule, causing it to become ionized. Non-ionizing radiation is a type of radiation that does not have enough energy to remove tightly bound electrons from atoms, therefore no ions are created. Examples of non-ionizing radiation include radio waves, microwaves and visible light. Since your RADAR emits non-ionizing radiation, it will not cause chemical changes in cells or damage DNA.
Earlier this year I was making my way up the coast with an owner on their new yacht. This beautiful vessel was fully equipped with a modern navigation system including the Garmin Fantom open array RADAR. It had been a misty morning with periods of dense fog and visibility at less than half a mile. The RADAR was working flawlessly as an invaluable tool for collision avoidance. We were intending a fuel stop along the central California coast, picking our way through the fishing boats and then making our way into the harbor in the soupy visibility. As we were docking and getting lines secured, the fuel dock attendant comes running out screaming, “you are killing me, turn that thing off!” It took a moment for his animated irritation to sink in for me to realize that I had not yet put the RADAR to standby as is the normal procedure when preparing for docking. RADAR now on standby and main engines shut down, I made my way on deck to prepare for fueling and the dock attendant was still muttering about how my RADAR will cause him to have headaches and eventually turn his brains to scrambled eggs. To be clear, I think his brains were well on their way to being scrambled but it has nothing to do with RF radiation and more to do with overuse of recreational substances. Of course, all this interaction brought a lot of questions from the owner regarding RADAR safety.
A Review On How RADAR Works
Modern RADAR is based on technology invented in the late 1930’s and is widely used for navigation, aviation, national defense and weather forecasting. Marine RADAR systems detect the presence, direction and range of nearby ships or other vessels and objects by sending pulses of high frequency electromagnetic fields (EMF). First the transmitter sends out narrow beams of electromagnetic radio waves in short or long pulses. These pulses are reflected off various objects and are then received by the RADAR receiver. The receiver accepts the returned energy of the radio waves and measures the time elapsed since the transmission. The distance, or range, of that object is calculated by measuring the total time the radar signal takes to make the trip to the target and back. Since the receiver knows the direction the antenna was pointing when the transmitted pulse was received it now has the bearing data to that object. By measuring the location of a target over time, the target’s recent track can be determined; and once established, the future path can be predicted. Now that the system knows the range and bearing, this digital information is processed and shown on the display.
The peak power of marine RADARS can reach up to 30kw, with average powers ranging from 1 to 25w. Under normal operating conditions, with the antenna rotating, the average power density of the higher power systems within a meter of the antenna is usually less than a few watts per square meter. In accessible areas on most watercraft, these levels would fall to a few percent of present public RF exposure standards. Also keep in mind, RADAR sets send electromagnetic waves in pulses not continuously, are directional, very narrow like the beam of a spotlight and the RF levels fall off rapidly outside of that main beam making the average power emitted much lower than the peak pulse power.
RADAR systems using different frequency signal and power levels have been introduced over the last eight or so years, led by the Simrad Broadband RADAR system, now in its fourth generation of production. The marine RADAR is classified under the x-band, 10 GHz, or S-band, 3GHz frequencies. The x-band, being of higher frequency, is used for a sharper image and better resolution whereas the S-band is used when in rain or fog as well as for identification and tracking. Then there are other systems such as Raymarine’s Cyclone and Garmin’s Fantom, which are both considered “solid-state” systems and use lower power levels to provide close-range performance. Furuno’s X-Class radar uses a three-gigahertz frequency to provide excellent targeting at both short and long ranges.
“Uninformed boaters often equate a marine RADAR with a microwave oven, and their body as a frozen bean burrito,” says Jim McGowan, marketing manager for the Americas for Raymarine. “It’s true that both systems use microwave energy and generate that energy using a device called a magnetron. For comparison purposes, most microwave ovens range in power output from 0.8 kilowatt (800 watts) to 1 kilowatt. The burrito analogy doesn’t hold up though because of a fundamental difference in the way a microwave oven works versus a marine RADAR. In order to heat your burrito, from the inside out no less, a microwave uses continuous-wave microwave energy. That means its magnetron is on and hammering away with 1 kilowatt of energy for its entire cook cycle. The microwave energy actually excites the molecules in the food, causing them to move faster and generate heat. This is what warms the food. The longer the exposure to the continuous-wave energy, the faster the molecules go and the hotter it gets.” That sounds unpleasant, to be cooked from the inside out. But it doesn’t happen to boaters. “The magnetron marine RADAR works differently in that it uses pulsed microwave energy,” McGowan says. “That is, the RADAR scanner actually turns itself on and off thousands of times a second. It does this so it can send a pulse, then listen for its faint echo returning. Depending on the range selected, the RADAR’s pulse could be short, long, or somewhere in between. But, even with a long pulse, the RADAR is only actually radiating for a few thousandths of a second at a time. Because of that constant on/off effect, the marine RADAR never generates power long enough to get the molecules moving in whatever objects are in the path of its beam. No heat means no cooking, burritos or otherwise.”
Specific Absorption Rate (SAR) is a measure of the rate at which energy (radiation) is absorbed per unit mass by a human body when exposed to a radio frequency (RF) electromagnetic field. SAR of at least 4 W/kg is needed to produce known adverse health effects in people exposed to RF fields in this frequency range.
The average SAR values for different devices are shown below and the SAR values can increase if you move close to the device and decrease if you move away from the device. The safe limit of 4 watts per kilogram provides a large margin for RADAR systems used in recreational boats. So, marine RADARS do not pose any adverse health threat to humans.
- Mobile phone = 1.6 W/m²
- Microwave oven (leakage) < 1 W/m²
- Wi-Fi router = 1.6 W/m²
- Marine RADAR = < 2 W/m²
Distance between the RADAR and the person is crucial. If you stand two meters away from the RADAR, you will get half the radiation of the person standing one meter away from it.
RADAR Is The Most Important Tool Of Your Navigation Suite
Although the primary use of the RADAR is for collision avoidance, your modern RADAR does many other things that no other electronic navigation device such as the GPS, chart plotters and AIS can.
See Where You Cannot
RADAR has the ability to see over the horizon where you cannot. Standing on the deck of the boat 16 feet up from the waterline, your horizon is less than five miles. Distance is derived from the formula for calculating distance in miles to the apparent horizon. Distance in miles = 1.23 x √H where H is the height above the water in feet. The square root of 16 is 4 x 1.23 is approximately five miles.
In contrast to that, RADAR can see over the horizon. Because the RADAR microwaves are less subject to atmospheric deflection than the visible light, the RADAR horizon is about 15 percent farther. Considering that your RADAR antenna is mounted 25 feet from the waterline and using the formula Distance in miles = 1.35 x √H we have an effective maximum range of 6.75 miles.
Beyond a certain distance, human eyes will fail to detect even large objects that are peeking above the horizon, but RADAR is not limited as our eyes are. Take a fast-moving boat with a flybridge height of nine feet above the waterline heading your way. Even though you might not be able to see it, a RADAR antenna mounted 16 feet above the waterline will be able to pick up that target at a greater range. Using the formula Distance in miles = 1.35 x √H1 + √H2 we get a RADAR range greater than nine miles (1.35 x (4+3)). Not only that, but the RADAR will also be able to track the target’s course and speed so you can make collision avoidance decisions well in advance.
See When You Cannot
Visibility can be compromised by darkness, fog, precipitation and even a faint haze. This is when some boaters deceive themselves by thinking they will be safe as long as they follow their GPS chart plotter route from waypoint to waypoint. The problem is that when following a GPS chart plotter route, it is not the charted objects that will be hard to avoid, it is the uncharted objects like other boats and floating debris that present a risk of collision. These are the conditions that make the RADAR most useful, provided that the operator is competent in using it.
Find A Fishing Spot
Let’s say you spot a target on your RADAR display, and it appears to be standing still or moving at trolling speed. You grab your binoculars and scan the distant boat, recognizing it as a fishing vessel with lines in the water. Or what if there is a cluster of targets, all relatively motionless, this just might be fishermen on a hot spot. If you decide that this is a spot that you will want to remember, then your RADAR can mark the GPS coordinates by using the VRM (Variable Range Marker) and the EBL (Electronic Bearing Line) to determine the exact distance and direction to the target fishing boat. Then it is easy to chart the coordinates of that prime fishing ground for future reference. Modern RADAR systems that are linked to your GPS also allow you to scroll the cursor over to the target and directly obtain a GPS coordinate for your new favorite fishing spot.
Many of the newer RADARS have a “bird mode” that automatically adjusts the receiver filters to look for clusters of birds on the surface up to five miles away. Birds on the surface may indicate baitfish below, and with baitfish near the surface we will find larger fish below.
Weather Alert (Squalls) RADAR sensitivity can be adjusted to indicate rain squalls in the distance, allowing you to analyze whether or not they are bearing down on your position. That might prompt you to batten down the hatches, alter your speed and course or initiate whatever heavy-weather tactics you decide to use to keep your boat and crew as safe as possible.
Enhanced Situational Awareness
On every boat that I operate equipped with RADAR, I place it in service even during clear weather and bright sunshine. Using the RADAR in daylight can enhance your situational awareness, alerting you to a boat overtaking from astern or quarter. The best time to practice using the RADAR is when you do not need it.
Marine RADARS send electromagnetic fields that are non-ionizing, meaning they will not cause chemical changes in cells and damage DNA, but at extremely high power they can cause a minor heating sensation on the skin’s surface. This sensation is not dangerous and will not hurt anyone. To produce any adverse health effects, RF exposure above a threshold level must occur. The known threshold level is the exposure needed to increase tissue temperature by at least 1°C. The very low RF environmental field levels from RADAR systems cannot cause any significant temperature rise.
Exposure to radio frequency, RF, fields above 10 GHz at power densities over 1000 W/m² can produce adverse health effects. However, even with the largest commercial RADAR used on large container ships, the power density is less than 10 W/m², which is far too low to produce adverse health effects.
To date, researchers have not found any evidence that multiple exposures to RF fields below threshold levels cause any adverse health effects, including cancer. No accumulation of damage occurs to tissues from repeated low-level RF exposure.
More information on marine electronics and RADAR in general can be obtained by contacting your local marine electronics installer. In the Delta, Marine Pros is available for questions and if you are in the Bay, you can contact Reliable Marine Electronics or Ian Wall at Star Marine Electronics.
A final thought about the uninformed fuel dock attendant; if you see an open array RADAR antenna spin you can guess that it is transmitting (not always on some RADAR sets) but what about the spinning antenna inside the radome that you cannot visually see to determine if it is actively transmitting?
Until next month I am going to enjoy a fine cigar and glass of port while watching my six-foot open array antenna spin in high-speed mode. Please keep those letters coming. If you have a good story to tell, send me an email email@example.com. I love a good story.