ALERT NEWSLETTER – May 2015

Hi everyone, I hope this finds you doing well & that you have been enjoying these spring days. Our May 12 ALERT meeting will feature our annual elections. If you are a paid up Operational or Supporting Member, which is a member interested in Amateur Radio, Skywarn or Emergency Communications, but doesn’t have a ham license (yet), you may vote in the 2015 – 2016 ALERT leadership elections. The officers will assume their positions at the July meeting. July is also when ALERT dues are due. Remember, if you want to respond to ALERT callouts or serve as an officer you MUST be current with your dues. Also, there will be a Board of Directors meeting preceding the regular 7 PM meeting at 6:30. I hope to see you there! …………………………………………………………………………………………………………. 50 Shades of GPS On April 9, 1998, one day after the F5 tornado, I was standing in the ruins of what had the day before been McDonald’s Chapel. The landscape was a scene on complete destruction, with no familiar landmarks. The only street sign left was mangled and folded together like praying hands, on which you could make out the words “Quebec Street”. What does one do when a community in an instant is made into a wilderness? How does one find their way, when nothing recognizable remains? It is in cases such as this, when the Global Positioning System proves an invaluable tool for emergency response. For, though the landmarks are gone, and the streets may be buried, it still remembers where you are and how to get you home. How much do you know about the GPS system? The GPS system, whose official name is NAVSTAR, is a Department Of Defense program, consists of a constellation of 32 satellites, which at an altitude of 17000 miles, orbit at 7000 MPH. The program was begun during the Nixon administration in 1973, and became fully operational in 1995. In 1996 President Clinton issued a policy directive declaring GPS to be a “dual use” system for both military and civilian use. GPS satellites circle the Earth twice a day continuously transmitting a signal to the Earth. The GPS receivers take these signals and compare the time that the signal was transmitted with the time that it was received. This time difference tells how far away the satellite is. With the distance from several satellites known, the receiver, using a mathematical principle called “trilateration” can determine the position and plot it on a map. Not unlike the system used by the old LORAN-C navigation system, which was decommissioned by President Obama in 2010. Being viewed as redundant alongside GPS after the Department of Homeland Security certified that LORAN was not needed as a backup for the GPS. This method of location is not the same as triangulation, where you take a compass bearing of an object from two or more locations, and where the bearings intersect on a map, the objects location is determined. With three satellites in view a GPS can determine latitude, longitude and movement. With four or more satellites in view, altitude can be determined. Newer units are very accurate because they utilize 12 parallel channel receivers, which, assuming the satellites are in range, allow them to receive 12 satellite signals simultaneously. These receivers are quick to lock onto signals, and are accurate to 50 feet. Differential GPS units correct GPS signal errors to an accuracy of 10 to 15 feet. The Coast Guard operates a DGPS correction service which consists of a series of towers that receive GPS signals and retransmits a corrected signal by beacon transmitters. To use this you need a differential beacon receiver and beacon antenna in addition to a GPS unit. GPS receivers with Wide Area Augmentation System – WAAS capability improve the accuracy to 10 feet. This system utilizes 25 ground stations spread over North America to correct the signals, and no additional equipment is required. Russia has a similar system called Globalnaya navigatsionnaya sputnikovaya sistema, or “GLObal NAvigation Satellite System” – GLONASS GLONASS consists of 24 satellites, and although coverage is better in the northern hemisphere, it has global coverage. The system was begun in 1976 and was completed in 1995. It then became neglected and deteriorated until 2001 when Vladimir Putin made the restoration of the system a top priority, which was completed in 2010. Like GPS, GLONASS was made available for public use in 2007 by a presidential decree by Vladimir Putin. GLONASS is the most expensive program of the Russian Federal Space Agency, with one third of its budget being dedicated to the system. There are some significant differences between GLONASS and GPS. GLONASS has fewer satellites in its constellation, with 24 satellites, versus the GPS constellation of 32. The GPS constellation circles the globe in 6 orbital planes, or paths of orbit, where GLONASS satellites use 3 orbital planes, in a slightly lower orbit. This means that with GLONASS, more satellites follow the same orbital path. For systems using GLONASS only, it may be more difficult to connect to available satellites. This could potentially lead to reduced positioning accuracy. The biggest difference between GPS and GLONASS is how they communicate with receivers. With GPS, satellites use the same radio frequencies but have different codes for communication. With GLONASS, satellites have the same codes but use unique frequencies. Despite these differences, GLONASS’s accuracy is comparable to that of GPS. You probably are already using GLONASS and are not even aware of it. Depending on the manufacturer of your smartphone, you may already have GLONASS capability in your device, Apple iPhones and a large number of Android devices use both GPS and GLONASS to ensure accuracy. If you are stuck in an area with a large amount of cloud coverage, or are surrounded by high-rise buildings, your device will use GLONASS in conjunction with GPS. This allows your device to be pinpointed by any of the fifty-five satellites around the world, increasing overall accuracy. However, GLONASS is typically only turned on when the GPS signal is poor in order to preserve the device’s battery. As for portable navigation devices, Garmin GLO is a portable GPS and GLONASS receiver which connects to a mobile device over Bluetooth, and provides better accuracy than any integrated receiver. GPS Quirks & Peculiarities A few years ago I was watching one of the “judge programs” that air in the afternoon. One Judge, a lady with an accent vaguely similar to Bugs Bunny was hearing a case where a gentleman was being sued for not fulfilling a promised work obligation. He admitted that he did not show up and do the promised work, and when asked why, he said he had entered the address in his GPS and it kept saying “no signal”. Hearing this, the Judge declared him a “liar”, since things like that certainly don’t happen with a GPS. She then asked the audience, saying with rolling eyes “has anyone here ever heard of such a thing?” This course, they thought this was ridiculous and laughed him to shame, and nodded their heads approvingly as the verdict went against the gentleman. Whether he was actually guilty as charged or not, I still don’t know, but, I distinctly remember saying to the TV “Oh yes they DO lose signals, you dimwitted wabbit.” As with all manmade devices, GPS units have their own quirks and peculiarities. Some common problems which will defeat a GPS’s accuracy or operation are: Atmospheric Delays – Satellite signals slow as they pass through the atmosphere, which affects the receiver’s calculation of distance from the satellite. The GPS system partially corrects for this type of error by using a built in model that calculates the average amount of delay. Signal Multipath – The GPS signal may reflect off of objects such as tall buildings or rock surfaces before it reaches the receiver. This effect increases the travel time of the signal, thereby causing errors. Receiver Clock Errors – A receiver’s quartz clock is not as accurate as the atomic clock onboard the GPS satellites. Therefore slight timing errors may occur. Orbital or Ephemeris Errors – Gravitational fields or solar storms can cause inaccuracies between the reported positions of the satellite and its actual location, for instance, during a solar storm the atmosphere expands outward into space, causing drag on the satellites temporarily slowing them. Number Of Satellites Visible – The more satellites that a GPS receiver can receive, the better the accuracy is. Buildings, terrain, electronic interference, or even dense foliage can block signal reflection, causing position errors or no signal at all. GPS units typically will not work indoors, underwater, or underground. Plus keep in mind that these satellites are not in a geosynchronous orbit, like communications satellites. They, being in a lower orbit are constantly changing position, in a never ending celestial shell game. Sometimes they just travel out of range. Satellite Geometry and Shading – this refers to the position of the satellites in relation to each other and the GPS receiver at any given time. The best satellite geometry occurs when the satellites are located at wide angles from each other. If they are too close to each other, signal interference can occur. Intentional Degradation of Satellite Signal – “Selective Availability” or SA is an intentional error that was introduced to GPS signals by the Department of Defense, to prevent our enemies from using our own GPS constellation for targeting weapons against us. The government turned off SA in May 2000, which improved accuracy, but, they can easily reintroduce the errors, if they determine that a probable threat exists. Radio Troublesome Traits – It should not be forgotten that GPS units (and cellphones for that matter) are, regardless of their sophistication, still radio receivers. Some are more sensitive than others and can pick up marginal signals better, and some are more selective than others and are less susceptible to interference from stronger nearby signals. With cellphones, to use old CB terms, some are “Alligator Stations”, transmitting big signals, but, having sorry reception, and others are “Elephant Stations”, with great reception, but, transmitting wimpy signals. Some are quicker to drop a call when the carrier is lost than others which might “keep the squelch open” longer waiting for the signal to return. Ordinary Electronic Problems – These would include electronic component failure, dead batteries, running over the poor thing with your truck, dropping it into the toilet and so forth. Can’t Find It Issues – Ever lose anything right at the wrong moment? For these reasons, though I certainly love my GPS, for some purposes, such as hiking, I actually consider it as a backup to being able to read and use a map and compass. Let’s talk about compass APPs on Smartphones for a moment. Whether you download a compass APP or one comes “factory built” in your phone, they both operate in the same manner and with presumably the same results accuracy wise. How does this device work? Smartphones have a small magnetometer that measures changes in the Earth’s magnetic field and an accelerometer that tracks the movement of the device. The accelerometer gets information regarding the phone’s position in space. The app combines the heading information from the magnetometer with the roll and pitch data from the accelerometer to work out the exact orientation of the unit as you move the device. This is all independent from GPS signals or cell tower pings, though some smartphones will also use GPS data to determine latitude and longitude. Are these compass apps accurate? Based on my own experimentation, the answer is “at best, more times than not”. I’ve seen them work fine one day and the next day have them indicate “north”, when it was pointing dead east. I’ve also seen them change orientation for no apparent reason and had them jump back and forth with no movement occurring or outside influence to explain the erratic behavior. I consider it usable, but, look at it with a jaded eye, remembering that it has some quirks. “Real” compasses have their quirks also, by the way. For instance, if you use one near a metal object or magnet (think cellphone speakers here) it will throw the needle off. This is called “magnetic deviation”. Also, there are geographic locations possessing “magnetic anomalies”, which are defined as “a local variation in the Earth’s magnetic field resulting from variations in the chemistry or magnetism of the rocks.” An example of this is at Goat Hill, the location of the Alabama State Capitol. No joking intended, there is a magnetic anomaly on the hill which causes compass errors. Though I can find no reference for this online, I know that there was, and presumably still is a USGS marker on the hill near the capitol indicating this, and the amount of error involved. Most compasses are usually slightly off target due to “magnetic declination or variation error”. The Earth’s North Magnetic Pole is not at the physical or geographic North Pole, but actually near Baffin Island in Canada. A compass does not point along lines of longitude, but, rather along the lines of the Earth’s magnetic field, which in the case of Central Alabama, are off 3 degrees to the west, and due to the Earth having a molten core, the lines are drifting slightly further westward each year. For short distance navigation, this isn’t a problem, but, for longer ranges, then you would have to offset your reading 3 degrees to the east for true North to match USGS maps and charts. Also, not all compasses are created with equal quality. When choosing one, take several off of the shelf and keep these three guidelines in mind. 1. Fancy looks, doesn’t necessarily mean fancy results. 2. They should all be pointing in the same direction. 3. After turning a 360 circle where you are standing, they should quickly return to the North position. Just remember “Mark’s Rule of Compasses” – “If they don’t work in Walmart, they won’t work in the field either”. I use a Silva brand compass, which has always served me well. It’s like with any device or technology. You need to learn and understand the limitations of the resources that you are using and then learn to work around those limitations. These, and having backup plans, are always keys to success. Just remember the quote from the great Yogi Berra – “You’ve got to be very careful if you don’t know where you are going, because you might not get there.” ………………………………………………………………………………………………………………. ALERT Sunday Night April Net Report Date NCS Checkins Traffic Apr 8 N4HEY 45 0 Apr 12 KK4YPK 41 0 Apr 19 KK4NGD 46 0 Apr 26 WD4NYL 42 0 ———————————————— TOTAL 174 0 ——————————————————- YEARLY TOTAL 778 0 ……………………………………………………………………………………………………………………………………………… Mark’s Almanac May is the fifth month & third month of the Roman calendar. May is named for the Greek goddess Maia, who was identified with, Bona Dea, the Goddess of Fertility, who was celebrated in May. Since ancient times the first day of the month, “May Day” has been a time of celebration. In Rome it honored Flora, the goddess of flowers. On May the fifth Mexican’s celebrate Cinco De Mayo, the celebration Mexico’s 1862 victory over Napoleon III’s forces at Puebla. This is not, as many assume, Mexico’s Independence Day, which is actually on September 16. Rainfall decreases in May as the Bermuda High strengthens & begins rerouting storm systems northward. The door opens to the Gulf of Mexico & Gulf moisture spreads northward over the continent. The center of maximum tornadic activity also shifts northward over the Nation’s Heartland. May is the peak tornado month, with a 42% increase over April’s amount. Eastern Pacific hurricane season begins May 15, and although the North Atlantic hurricane season has not arrived, occasionally a tropical system will form in the Gulf of Mexico. In 110 years there have been 14 named storms. Looking skyward, Mercury is rising from the glow of sunset, and on May 7 will reach his highest elevation over the Western horizon, or “greatest eastern elongation” of 21.2 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the evening sky. Look for the planet low in the western sky just after sunset. Mercury will soon sport a new crater, as the US Messenger space probe will impact on Mercury on April 30, having run out fuel, successfully ending its mission having orbited the planet since March 18, 2011, and returning over 250,000 pictures of the heavily cratered planet. Venus, the “Evening Star”, blazes in the West during and after evening twilight, setting in the west-northwest nearly two hours after dark. Mars is deep in the sunset near Mercury. Jupiter in Cancer is high in the South as the first evening stars appear, and is the second brightest object in the evening sky, after Venus. Saturn in Scorpius rises around 10 or 11 PM and is highest in the south in the early morning hours. The ringed planet will be at its closest approach or “opposition” to Earth on May 23rd and its face will be fully illuminated by the Sun. It will be brighter than any other time of the year and will be visible all night long. This is the best time to view and photograph Saturn and its moons. A medium-sized or larger telescope will allow you to see Saturn’s rings and a few of its brightest moons. I guess the term “ringed planet” is somewhat out of date now, since US probes detected a faint ring system around Jupiter and a ring system around Uranus. But, their rings you can’t see from Earth, Saturn’s you can. Uranus is deep in the glow of the Sun. Neptune is low in the East at the beginning of dawn. Full Moon will occur May 3th at 10:32 PM CDT. May’s Moon is “Flower Moon” in Native American folklore, but has also been called “Corn Planting Moon” & “Milk Moon”. The Eta Aquarids Meteor Shower, a minor shower, will peak May 5 & 6 with 30 meteors per hour. It is produced by dust particles left behind by comet Halley. The nearly full moon will be a big problem this year blocking out all but the brightest meteors. If you are patient, you should still be able to catch a few good ones. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Aquarius, but can appear anywhere in the sky. New Moon will occur May 17 at 11:13 PM CDT. This is the best time of the month to observe faint objects such as galaxies and star clusters, as there will be no moonlight to wash out the evening sky. 1831 planets beyond our solar system have now been confirmed as of April 23, per NASA’s Exoplanet Archive http://exoplanetarchive.ipac.caltech.edu/ ……………………………………………………………………………………………………………………………………… This month’s meeting will be on May 12 at 7PM at the National Weather Service Forecast office at the Shelby County Airport. If for some reason you cannot attend the meeting in person, you can still participate via telephone. The teleconference number is 1-877-951-0997 & and the participant code is 741083. Hope to see you there! Mark / WD4NYL Editor ALERT Newsletter www.freewebs.com/weatherlynx/ Mark’s Weatherlynx Weather Resource Database