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Volume 11, No. 1 |
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President, Mr. Ronald Hatch, Navcom Technology, Inc. |
Q & A: WAAS and DGPS Maritime Use Discussed Departments: From the ION President: Assessing the Past, Looking Ahead Congressional Fellow Report: A Once-in-a Lifetime Experience Portney’s Corner: The Lost Sub From the ION Historian: Navigation Jotto GNSS Around the Globe: News in Brief, Section News, Launches, and more |
Galileo Forges Ahead With New Release of Funds
Galileo, Europe’s global satellite navigation system, leapt an important hurdle on April 5, 2001, when European Union Transport Ministers agreed to make available r100 million for the start of the program. The ministers will decide on the release of a further r450 million at their meeting next December, when they will also approve the establishment of an entity to manage the program. Moreover, the ministers agreed to make the formal decision on the deployment of the full constellation by the end of 2003.
In February 2001, the European Space Agency (ESA’s) Navigation Program Board approved the funding for the initial design study and additional European Space Agency funds are to be released. The Transport Ministers’ decision provides the framework for the long-term implementation of the two European satellite navigation initiatives, Galileo and EGNOS, and identifies issues that remain to be resolved during 2001. These include the following:
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From the ION President: Assessing The Past, Looking To the Future
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The past year has been an exciting time for navigation, particulary for GNSS - especially with the GPS modernization underway, the ongoing GPS III requirements development program, and a European proposal for the Galileo constellation. I am happy to report that ION conferences continue to be the key forum to report on these activities and overall the ION and its programs are doing very well.
New Initiatives
Our first year of the ION congressional fellow program has been extremely successful, and Phil Ward has had a rewarding experience supporting Sen. Inhofe (which Phil will elaborate on in his report). I think Phil has represented the ION well.
During this past year, we initiated the ION Conference Committee, which is chaired by the ION executive vice president and includes the ION technical area representatives as members in order to assist in identifying future session topics and programs. Additionally, it is important to attract new participants to the role of session chair/co-chair. The first opportunity to actually apply this effort was for the ION GPS 2001 conference. You will notice many new session chairs and more abstracts submitted than ever before (close to 500). There is still some work to be done in order to have the role of the ION Conference Committee better integrated into the process of putting together a conference.
Increased Participation
The ION Conference Committee also is part of our effort to increase participation from Council members and assign defined roles and responsibilities. The ION National Office has worked to put together a document defining the roles and responsibilities of each Council member. Hopefully this will be helpful
to incoming members of the Council and will serve as a reminder to others.
Through the Strategic Planning Committee, we have begun to focus on ION investments and identifying goals for special programs that could rely on investments, which are above what we need for the Reserve Fund. I would like to thank Mike Braasch, the ION finance chair, for his efforts in this area. The Strategic Planning Committee also has taken on the task of trying to identify new co-sponsors for our meetings in an effort to achieve regional balance for meeting locations.
The ION National Office continues to serve our membership well by providing support to ION sections, committees and program chairs, which has helped increase the number of volunteers and their willingness to support ION programs. I had the opportunity to visit the national office several times during the past year and have been impressed by the efficiency of its operations and how well managed it is.
Increased Visibility
The ION National Office also has increased the visibility of ION by participating in meetings such as RTCM, RTCA and GNSS 2001. The Web site has continued to improve and a major upgrade is about to come on line with many new membership services. We also hired Rick Buongiovanni to become a full-time member of the ION staff. He will be a great addition to support the ION’s information technology needs.
In closing, it has been a pleasure to serve as ION president for the past year, and I would like to thank the executive committee and council for their dedicated efforts. I also would like to offer special thanks to the ION National Office for all the support the staff has given me.
I have enjoyed working with Ron Hatch as our executive vice president and head of the Strategic Planning Committee, and the ION will be well-served with him as president for the next year.
President, 2000-2001
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Executive Vice President: Dr. Rudy Kalafus Treasurer: Mr. Larry Hothem Eastern Region Vice President: Ms. Sally Frodge Central Region Vice President: Maj. John Raquet Western Region Vice President: Dr. A.J. Van Dierendonck Immediate Past President: Ms. Karen Van Dyke
Facsimile: 703-683-7105 Web site: http://www.ion.org E-mail: membership@ion.org
Technical Director: Carl Andren Office Manager: Jennifer Murphy-Smith Assistant to the Technical Director: Miriam Lewis Meeting Services/Author Liaison: Connie Mayes Member Services/Registrar: Wendy Hickman Graphic Design/Editor: Paula Danko Information Systems: Rick Buongiovanni |
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From the ION Congressional Fellow: A Once-in-a Lifetime Experience!
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In my second report, I described my ordeal of being on this side of the interview process for the first time in over thirty years. Perhaps you sensed my anxiety: I had not found a suitable assignment on the Hill by the deadline for my article. Happily, you learned from the editor’s note that I was offered a position with Sen. James M. Inhofe (R-Okla.). In case you missed the paradox in my last report, I described what seemed to me a futile effort soliciting a science congressional fellowship position with any member who sits on the House Armed Services Committee (HASC) or the Senate Armed Services Committee (SASC), but I actually received an offer from a very high ranking senator in the SASC! It just so happens I am the first science fellow that Sen. Inhofe has asked to serve on his staff, so it was just a case of timing and good fortune for me. As I have said to many close friends in the ION "even a blind squirrel sometimes finds an acorn!"
How Does GPS Fit Into This Picture?
My original reasoning was simple: My professional expertise is in GPS. GPS is a Department of Defense (DoD) satellite navigation system and the HASC or the SASC are where legislation and hearings that relate to GPS would happen. It took me a while to learn that the DoD provides hand picked officers from the Pentagon as military congressional
fellows for every member of the HASC and the SASC and there is seldom room for more than one fellow. In addition, the military legislative assistant (MLA); i.e., the permanent staff member responsible for HASC or SASC activities, is usually a retired military officer. Thus, the MLA is not inclined to either know about or look for science fellows. It turns out
that my original reasoning ultimately paid off, even though I had long since given up interviewing any more members on the HASC or the SASC by the time I received the offer from Sen. Inhofe.
How Did I Get This Assignment?
Here is what was happening behind the scenes in Sen. Inhofe’s office. Sen. Inhofe was among my top five members at the beginning of my interview process, so I delivered my curriculum vitae (CV) to his office in January. Unknown to me, the MLA transferred from Sen. Inhofe’s office to Rep. J.C. Watts (R-Okla.) office in February. That left only the military congressional
fellow, Major Dave Teal, running the SASC show for Sen. Inhofe. This difficult situation plus my CV made it desirable to the legislative director (LD) and chief of staff (CoS) to consider having a science fellow and a military fellow help with the SASC tasks while they searched for a new MLA. With persistence and luck, I managed to get an interview with Sen.
Inhofe’s legislative director, Chad Bradley, his chief of staff, Glenn Powell, and his military congressional fellow, Major Dave Teal, all on the same day. Even though, they spent nearly two hours with me and the interview went great, it was several weeks before a decision was made. It turned out they were trying to find an opportunity for Sen. Inhofe to meet
me. Finally, Sen. Inhofe told Bradley to make me an offer based on the good reports from the three of them. Ironically, the day before that offer came, I received two offers from the House side, and the day after I started to work, I received another offer from the Senate side. These events helped my drooping morale abundantly!
Benefits of Twenty-Twenty Hindsight
Had I only known about the best timing for my office visits or calls, I think I could have cut the decision time by more than two weeks. Between Tuesdays and Thursdays, there is so much activity for every staff member, especially the LD and CoS, that they are hard pressed to even take a lunch break, much less respond to phone calls or
front office requests from walk-ins to get on their interview calendar. Also, it is greatly beneficial to have some inside help. I will be in a position to help in that regard for our next ION congressional fellow.
Obstacles to Placement
You soon learn that your greatest enemy to placement as a science congressional fellow is the lack of office space (after all, you represent a zero staff budget impact to the member). So you learn to concentrate on ranking members that have more office space. New members get the smallest offices so their personal staff works in cramped quarters. Senate
members have more space and larger staffs than House members. Your next worst enemy is lack of recognition of the value of science congressional fellows. Part of the reason is the youth, lack of post-graduate degrees, and lack of experience of the member’s personal staff. About half the staff in the Senate and House are under ages 35 and 30, respectively.
There is also a high turnover rate-about 40 percent per year. They work in an office environment characterized by long and erratic hours, cramped working conditions, conflicting job requirements and, with few exceptions, fairly low pay.
Profile of a Typical AAAS Congressional Fellow
Most of the AAAS congressional fellows come from mid-career academic backgrounds, typically post-doctoral candidates. Of the 39 AAAS congressional fellows, I count 26 who work for Democrats and seven (including myself) who work for Republicans. The remaining six have taken assignments on committees or with the Library of Congress Congressional
Research Service. Even though the Democrats are presently the minority party in both Houses, they were clearly more pro-active in recruiting science congressional fellows during our orientation session in September.
"Baptism of Fire"
I received a "baptism of fire" my first week in my new position. Dave Teal, the DoD fellow, had been given a much needed week off to go on a family skiing trip to Breckenridge, Colo., with his wife and her parents. I spent the first day meeting staff, filling out paperwork, getting my badge, learning about the peculiarities
of the Senate staff computer programs and visiting the offices of the other members who made me offers. I wanted to express my gratitude in person for their confidence in me and to explain my decision to go with Sen. Inhofe. The second day, I learned that Sen. Inhofe would be taking Sen. John Warner (R-Va.), Chairman of the SASC, to Oklahoma on a
whirlwind tour of several military bases that Thursday. I was tasked to provide up-to-date "fact sheets" on Tinker Air Force Base (AFB), Vance AFB, Altus AFB and Ft. Sill Army Base. Fortunately, Ellen Brown, our military legislative correspondent, came to my aid. She contacted the previous MLA who provided a series of web addresses and she put me in touch with
the Air Force and Army military liaison offices on the first floor of Russell Senate Office Building. Those resources provided all the information I needed and I put it together. The senator liked it! Then I learned that Teal’s father-in-law had a serious skiing accident and Teal would be delayed for another week. I look back on that experience now and I
chuckle because it forced me to move faster and interact with the personal staff at a much faster pace than I thought was possible for me.
Off to a Good Start
My first contact with Sen. Inhofe was by phone on a Tuesday of the second week on my new job. I was expecting a return call on another task I was pursuing. I did not recognize the senator’s voice and he seldom announces who it is on his end of the line. He opened with "Phil, we need to meet each other soon." When I asked if this was the person I was expecting, he then told me "No, this
is Jim Inhofe. Do you have the notes you prepared for me in front of you? I have some questions." He had just stepped out from the Senate chamber into the Republican cloak-room to call me. He mistakenly thought I was the one who had prepared the talking points for two side meetings scheduled with lobbyists
in two different Capitol meeting rooms later that day, the first with the Uniformed Services Disabled Retirees and the second with the American Legion. Well, my initial reaction was to say how much I looked forward to meeting him in person. Then I realized that I had no idea what he was talking about, so the next thing I said was that I did not have the
document in front of me but would locate it and call him right back if he would give me the number where he could be reached. Again, Ellen came to my rescue. She was the author of the material.
Less than an hour later, I met Sen. Inhofe in person in his office just a short walk down the hall from my office. He had a delegation from Oklahoma City waiting in his office, so he sent Ellen and I ahead of him to the Capitol to meet with the first group. I had my first ride on the Capitol subway and, I am ashamed to say, my first visit inside our nation’s Capitol. Sen. Inhofe joined us later, then I rode back with him and we had our first opportunity to talk at length. That is when he found out I was a GPS expert. Since he has been a pilot for more than 30 years, he is a strong supporter of GPS. Our relationship was off to a good start.
What Makes This Job So Great
I have heard many congressional fellows complain that they never see their member. That has not been my experience at all. The military legislation staff supports Sen. Inhofe in every area related to his very important roles on the SASC, including chairman of the Readiness and Management Support Subcommittee, ranking member on the Air Land Subcommittee and member of the
Strategic Forces Subcommittee. Until our new MLA showed up two weeks ago, Dave or I would support all SASC or subcommittee hearings. This requires that you read the written testimony of the witnesses as well as all related material you can get your hands on, then draft questions (that Sen. Inhofe may or may not ask after the oral testimony). You try to get the material to your member at least a
day before the hearing. You must be prepared to brief your member before the hearing starts, escort him to the hearing room in one of the Senate office buildings (Hart, Dirksen or Russell), and sit directly behind him ready to answer any questions he might have during the hearing. You also keep notes during the hearing in case the media staff decides to
issue a press release.
When Sen. Inhofe is scheduled to appear on "Crossfire" or similar news interviews related to a military topic, the "war room" (our nickname for the military legislative staff office) prepares "talking points" in support of that topic. The research is similar to that performed for SASC hearings, except that you cannot predict what questions will be asked, so you try to prepare for all relevant issues on the subject matter. You are very interactive with your member when such events are in the preparation stage!
The senator’s calendar is usually full with debates and voting on the Senate floor plus outside events and speeches, either here or in Oklahoma, or both at the same time. The only real problem with Sen. Inhofe is that there is only one of him! So his staff, including his congressional fellows, fill in for him with meetings that he cannot attend or can only attend for a few minutes.
There is a computer program called Intranet Quorum that keeps us informed about his schedule and the support he will need. For example, many lobbyists visit his office looking for support for their programs. When these relate to the military and involve scientific or technical matters, I get the nod to take them. The follow-up to these briefings is extensive, but fortunately there is a system in place to rank and process them.
I have touched on only a few of the many activities that touch my life on the Hill. There are also some nice "perks" that come with the territory such as invitations to elegant receptions, exciting tours and interesting presentations by high-ranking persons. I could completely fill my calendar with these activities if there weren’t so many other things to do. I carefully select only the ones that are definitely "can’t miss" events and yet I still barely find the time and energy to attend.
I hope this gives you some idea of what this wonderful assignment is all about. I am grateful to the ION for this once-in-a-lifetime experience!
Removal of GPS Selective Availability: Effects on WAAS
By Bill Klepczynski
Selective availability (SA) on the Global Positioning System’s (GPS) Standard Positioning Service (SPS) ended a few minutes past midnight Eastern Daylight Time after the end of May 1, 2000. With respect to the navigational information that the FAA’s Wide Area Augmentation System (WAAS) transmits to the civilian user, there will be some effects but none that will dramatically alter its current development and implementation or its reason for existence. Even with SA removed from the GPS signal, the Standard Positioning Service of GPS will not be able to meet the navigational requirements of civilian aviation.
Civilian aviation requirements for navigation include accuracy (which is addressed in this article), integrity, availability, and continuity. Consequently, the need for the WAAS still exists.
A Rare System
GPS was one of those rare systems whose operational performance exceeded its designed performance. The designers of GPS knew that this would be the case. However, the technology to degrade the systems to its advertised levels of accuracy could not be implemented with the deployment of the developmental GPS Block I satellites. Consequently, the civilian user started
to use the system during its initial state of operation with the precision and accuracy that is now available. They were very happy with the 20 meters or so of accuracy that they were achieving. It was similar in performance to Loran-C, but it was global.
Because accuracy is addictive, the civilian users were very upset when SA was turned on in March of 1990 with the Block II Satellites. The level of accuracy achievable with the SPS was reduced to the design level of 100 meters.
It should be kept in mind that prior to 1990, the civilian community had learned much about the characteristics of the system. As a result, when SA was turned on they were able to develop methods for augmenting the transmitted GPS signals with additional information in order to improve its level of performance back to that which was previously achievable. In fact, the techniques developed to augment the GPS SPS had achieved better performance than that attainable with the Precise Positioning Service (PPS), the navigation capability reserved for the military.
The PPS was not then, and even now, able to meet the requirements for all levels of flight. This deficiency in GPS led to the development of the WAAS, a differential system that improves the SPS to a level of accuracy necessary for civilian aviation and, at the same time, exceed the accuracy attainable with the PPS. This is a very important point. In order to achieve CAT I precision approach landings, position will have to be determined to better than 7 meters. Even now, the PPS can practically achieve those levels. However, testing has indicated that the WAAS can adequately achieve this level of performance. In order to achieve Cat III landings, 1 meter is necessary. The LAAS will achieve these levels but the GPS PPS cannot.
SA Signal Degradation
SA can degrade the GPS signals in two ways. One way is to desynchronize the GPS clocks that control the navigation signal transmissions. This affects the performance of the navigation solution that takes place within the computer in the navigation receiver. In order for the navigation receiver to determine
its position, it assumes that the signals coming from the GPS satellites are synchronized, i.e., they all keep the same time. The other way SA can degrade GPS accuracy is to introduce an error in the transmitted position of the satellite. The user receiver and its computer need to know where the satellite is
in order for it to compute its position.
SA On vs. Off
With SA turned on, the mission of the WAAS was to transmit information on the amount of SA to the user by computing better estimates of where the satellite is and by computing the amount by which the GPS Master Control Station (MCS) offset the satellite clocks. The WAAS Master Station (WMS)
would then transmit this information to the user. In addition, the WAAS Reference Stations (WRS) were making measurements on the amount of retardation that the GPS signals were undergoing as they traveled through the ionosphere. This information was also transmitted to the user.
With SA off, the largest error that contributes to the error in the user’s determined position is the lack of knowledge of the retardation that the GPS signals undergo as they travel through the earth’s ionosphere. As the GPS signals travel through the atmosphere, the signals interact with the charged particles in the ionosphere and are slowed down. The PPS actually measures the amount of retardation by using two different frequencies. The SPS only estimates the amount of the retardation by using a theoretical model. The SPS will never be as accurate as the PPS because of this. The model can only estimate the amount of retardation by about 50 percent. The total retardation can amount to 25 to 40 meters, on occasion, but is usually around 10 to 20 meters. At nighttime, it is even less.
With SA off, the WAAS will still transmit information on the location of the GPS satellites because it provides a check on the accuracy of the transmitted positions that the GPS MCS cannot check in real time. It will also compute and transmit the messages that contain the clock offsets because, even though they are not being degraded and not changing dramatically, the satellite clocks still have to be monitored. Their performance can degrade with time. The WMS can transmit this information to the user before the GPS MCS can. However, its most important mission will now be to transmit the ionospheric corrections that the user needs, but cannot measure himself, to determine an accurate position. One must keep in mind that the aviation receivers currently in use are single frequency receivers. They cannot measure the ionospheric retardation that the GPS signals undergo.
Dr. William J. Klepczynski is currently with Innovative Solutions International, Inc. where he provides consultation for the Wide Area Augmentation System architecture and systems design, analysis of the timing of the WAAS network and the time transfer capabilities of the WAAS.
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A Q & A With the U.S. Coast Guard
WAAS and DGPS Maritime Use Discussed
WHEN THE FEDERAL AVIATION ADMINISTRATION (FAA) ANNOUNCED that their space-based, L-band Wide Area Augmentation System (WAAS) became available for use by &qupt;some aviation and all non-aviation" users, it prompted numerous inquiries to the Coast Guard regarding the maritime use of WAAS and the status of the Coast Guard DGPS system. The following questions and answers are directed at helping to clarify the status of these two systems for the mariner.
1. Why did the Government design and build two different GPS augmentation systems?
The 1994 National Telecommunications and Information Administration (NTIA) Technical Report to DOT on a National Approach to Augmented GPS Services studied the necessity of expanded government efforts in providing DGPS services. Its goal was to recommend the optimum integrated system to meet aviation and terrestrial navigation needs. A variety of systems were being proposed at the time. The study concluded that a combination of two systems, the FAA’s Wide/Local Area Augmentation Systems (WAAS/LAAS) and the USCG’s DGPS system, was the optimum mix. This integrated system, consisting of the L-band line-of-sight WAAS for aviation users, and the terrain-following medium frequency DGPS for maritime and terrestrial users, meets the vast majority of the nation’s precise navigation and positioning needs.
2. Is WAAS currently certified for maritime navigation?
No. WAAS is not yet fully operational and is currently in a testing status, undergoing further development. It is not certified for use as a safety of life navigation system in the maritime navigation environment. WAAS may be used, with caution, in the maritime environment to improve overall situational awareness, but it should not be relied upon for safety-critical maritime navigation. The Maritime DGPS Service, on the other hand, is fully operational and meets all the standards for the harbor entrance and approach phases of navigation.
3. After WAAS reaches initial operating capability (IOC) in a few years, will it be suitable for maritime navigation?
WAAS is not optimized for surface (maritime and terrestrial) use, rather, it was designed primarily for aviation use. It is intended to eventually support aeronautical enroute through precision approach air navigation. The current WAAS test signals are transmitted by two geo-stationary satellites on a line-of-sight, L-band radio frequency. This means that if anything obstructs the view of the portion of the sky where the satellite is, the WAAS signal will be blocked. Since geo-stationary satellites are positioned over the equator, the farther north users are, the lower the geo-stationary satellites are in the sky-increasing the likelihood of an obstruction. In contrast, the medium frequency (285-325 kHz) radio beacon-based Maritime DGPS Service is optimized for surface (maritime and terrestrial) applications because it’s ground wave signals "hug the earth" and wrap around objects.
This means that the Coast Guard DGPS system is well suited for the marine environment (down in the "ground clutter") where a geo-stationary satellite can be blocked by terrain, harbor equipment and other man-made and natural objects.
4. Can the Coast Guard’s DGPS system be used by aviation?
That’s up to the FAA. However, the Coast Guard’s system was designed with the surface (maritime and terrestrial) user in mind. It was neither designed nor intended to meet aviation requirements. Although aviation users could potentially get some modest benefit from the Coast Guard’s DGPS for applications such as surface traffic management at airports or General Aviation, it could not attain the type and level of aeronautical service for which WAAS and LAAS are designed, without significant re-engineering.
5. Is the Coast Guard DGPS system a "transient technology" that is here today but will be gone tomorrow?
No. DGPS has already been adopted globally as an international maritime standard established by the 1994 International Telecommunications Union document ITU-R-M.823. It meets IMO Resolution A 815(19) standards for navigation in harbor entrances and approaches. Over 40 nations have fully embraced this robust technology and are implementing DGPS services identical to our own.
6. Which system is more accurate, WAAS or DGPS?
On the average, WAAS and DGPS accuracy are virtually the same, although DGPS accuracy is better when the user is near a DGPS transmitting site. The WAAS architecture is designed to provide uniform 7m accuracy (95 percent) regardless of the location of the receiver - within the WAAS service area. DGPS is designed to provide better than 10m navigation service (95 percent), but typically provides better than 1 meter horizontal positioning accuracy (95 percent) when the user is less than 100 nautical miles from the DGPS transmitting site. Accuracy then degrades at a rate of approximately 1 meter per hundred nautical miles as the user moves away from the transmitting site. A total of 56 maritime DGPS sites provide coastal coverage of the continental United States, the Great Lakes, Puerto Rico, portions of Alaska and Hawaii, and portions of the Mississippi River Basin.
Conclusion
Once WAAS becomes fully operational, the combination of Coast Guard and FAA systems is expected to provide a robust, complementary service to all modes of transportation. We look forward to the day that industry provides the public with a fully integrated receiver, one that uses all
available radionavigation systems to provide unprecedented accuracy, integrity, and availability. Despite the differences between DGPS and WAAS, it should always be kept in mind that both services ultimately rely upon a single navigation system—GPS—which is vulnerable to
interruption at any time.
This lends additional credence to the recommended practice of using all available means of navigation and not relying upon any single system. Remember, prudent mariners will always keep looking out the window!
CDR Curtis Dubay and LT Terry Johns, United States Coast Guard
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Portney's Corner: The Lost Sub Quick Fix
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A submarine surfaces to obtain a quick fix to avoid being detected. Sunset is imminent which permits the submarine’s navigator to utilize a technique evolved in the 20s - the one-body fix. He recognizes the utility of the astronomical triangle in Figure 1 in yielding latitude by measuring the rate of change of a celestial body’s elevation angle while
knowing its azimuth. It is March 21, 1945 (vernal equinox) and the azimuth of the Sun is due East at sunrise and due West at sunset throughout the world. The equation for this technique is as follows:
Where L is latitude, dh/dt is rate of change of the body’s altitude and Zn is the body’s azimuth. Since the azimuth of the Sun is either 090°(at sunrise) or 270° (at sunset) at the equinox, the csc Zn term becomes unity and the equation reduces to simply as:
The dh/dt term (actually a partial derivative term we will find in the derivation) is in units of arcmin per sec and requires the conversion factor of 4 sec/arcmin. Using a stopwatch the navigator times the transit of the Sun’s disk through the western horizon at sunset (duration of time between the lower limb and the upper limb of the Sun touching the horizon). The diameter of the Sun is 31.8 arc min. The elapsed time of the measurement was 184.2 seconds. What is his latitude?
Where GMT is the local observation of sunset and GMT sunset is the time of sunset at Greenwich. Sunset at Greenwich is 1814. Local sunset was 0516.5 GMT. What is his longitude? At what latitude(s) is this measurement impractical?
A: 48° 55' N, 160°00' W, avoid the equator and polar regions
B: 47°30' N, 168°00' W, avoid Tropic of Cancer or Capricorn
C: 46°47' N, 167°30' W, avoid equator region
D: 46°20' N, 165°37.6' W, avoid the equator and polar regions.
We recognize that the use of differentiation introduces errors (owing to the "noisiness" of the process) and will yield an approximation of the navigator’s latitude.
The one-body fix was first discovered by the American mathematician Edward J. Willis and disclosed in 1928. Admiral Byrd and Captain Weems attempted to use this procedure by observing the Sun from the open hatch of a seaplane. The results were very discouraging. An early single shot bubble sextant was used. This procedure requires accurate knowledge of the azimuth of the observed celestial body. Inertial quality instrumentation would be required to establish the precision in the azimuth observation necessary to obtain accurate latitude. For this Portney’s Corner, we avoid this difficulty by selecting the equinox period where the knowledge of azimuth of the Sun is known at sunset (270°) and sunrise (090°) throughout the world to be due West and East respectively when the submarine surfaced.
It is readily apparent that the very low latitudes, where the cosine of latitude approaches unity, are to be avoided in using this procedure as one encounters the 1-cosine effect for small angles making it difficult to establish latitude with certainty. After spring and through the summer, at higher polar latitudes, there is either continuous twilight or sunlight with no setting of the Sun or the duration of sunset is very long. After fall and during the winter (in the northern hemisphere), the Sun is always below the horizon in the polar region. The derivation of the equation for finding latitude from the one-body fix is shown as follows:
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Bibliography
Bowditch, Nathaniel. American Practical Navigator. Washington: U.S. Navy Hydrographic Office, 1958.
Weems, P.V.H., Captain U. S. Navy (Ret.) and Captain R.E. Jasperson, U.S. Navy (Ret.). "One-Body Fix." United States Naval Institute Proceedings June 1957.
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From the ION Historian
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is a nice, simple, family word game. It is generally played by two people and it requires only a pencil and a paper.
Each person thinks of a word, typically from five to seven letters, and the other person must guess the word. The process of guessing
the word is accomplished by having each person alternately writing down a word, and the other person scoring how many of the
correct letters are in the correct position. For instance, if Player A’s secret word was HISTORY and Player B wrote down MYSTERY, then
Player A would tell Player B his score was four. Similarly, if Player B wrote down RHYMES he would get a score of zero.
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Unfortunately, although JOTTO is a nice, simple, family game, my family is not exactly a nice, simple family. As a matter of fact, when it comes to JOTTO, my family is a bunch of competitive, conniving snip-snaps. My wife only plays JOTTO as a diversification from clothes shopping. She uses her shopping sprees to uncover obscure words that she can employ against me in JOTTO. In our last two JOTTO clashes she stumped me with qiviut (a cashmere-like wool of the undercoat of the musk-ox) and with viyella (a twill-weave cloth of 50 percent cotton, 50 percent wool, designed to look like all wool flannel). My daughter considers herself a sophisticated patron (with my money) of the arts. She frustrates me with words like gouache (a method of painting in which watercolors are mixed with gum arabic to make them opaque) and claque (a group of paid applauders in a theater). My son is just plain unsavory in his quest to humble me. He has stooped low enough to revert to the last word in the dictionary, zymurgy, (the applied chemistry of fermentation processes) and to what he claims as the midpoint in the dictionary, lytta (a cartilaginous or fibrous rod embedded longitudinally in the tongue of dogs and several other carnivores). It may be a mystery to you what this has to do with navigation history. JOTTO, it turns out, is one of the few areas that I derive some benefit from my vast repository of otherwise useless knowledge in navigation history. Navigation devices like alidade (a sighting device that rotates over a scale, fitted with a small telescope or two pinnules) and pelorus (a compass fitted with an alidade for determining the bearing of a distant object) are particularly effective for me in JOTTO. I like those words because they frustrate my family by having many simple vowels in the middle of the word. Often my family adversaries are able to get five or six letters rapidly, raising their hopes and expectations for a knockout victory over me; only to be hung up for an eternity trying to determine the entire word. Sometimes an ornery sore loser might question the validity of one of my navigation history words and challenge me to provide a definition. This allows me to bask in the thrill of victory as I pull out my navigation reference which clearly states that a plough is a sixteenth and seventeenth century angle-measuring instrument that could be used either as a back-staff or as a cross-staff. See the figure and inset from Peter Ifland’s "Taking the Stars" for more information on the plough. |
A square staff 2 1/2 to 3 feet in length is fitted with a horizon vane, A, and a small arc spanning 85°. The scale is divided into units of 10° and is calibrated to read both altitude, a, and zenith distance. A shadow vane, B, can be positioned along the arc depending on he altitude of the sun. A sight vane, C, is mounted on a carrier that slides along the staff over a scale divided in degrees and minutes, starting with 5° or 6° and extending to 10° or 12°. Adjusting the sight vane along the staff causes the angle CAB to change slowly, thus providing a fine adjustment to the sight.
To Take a Sun Sight With a "Plough" |
Section News
NEW ENGLAND SECTION of the ION is active and healthy: membership is steady at roughly 150. Most members are located in the vicinity of Boston, but some are located in smaller concentrations near Providence and Newport, R.I., and several cities in Connecticut, particularly around New London, as well as from Maine, New Hampshire, and Vermont.
The New England Section hosts technical meetings every other month during the academic year. This year topics have included novel navigation ideas from the MIT Media Lab, tours of the Haystack Observatory in Groton, Mass., and tours of the Coast Guard R&D Center in Groton, CT. The next technical meeting is to be hosted by the MITRE Corporation in Bedford, Mass., and will cover current developments in GPS. Elections of officers for the 2001-2002 academic year will take place at a special program meeting in August.
PHILADELPHIA SECTION. On May 24, the reactived Philadelphia section met. John Lavrakas spoke on "Establishing a National Positioning Navigation Timing (PNT) Service," including aspects of GPS modernization, WAAS, LAAS, NDGPS and how a national service might be provided. Even though this section is hampered by large geographic separation between members, thirty members of local chapters of the IEEE, the AIAA and the ION attended. Combining the sponsorship of these meeting not only makes them well attended, but also allows for cross-discussion and recruitment of professionals from other technical organizations with similar interests.
WASHINGTON, D.C. SECTION. The first meeting to reactivate the Washington section was held on May 30 at the USNO. This kick-off meeting was a huge success due largely to the efforts of Section Chair Jim Doherty and Francine Vannicola of the USNO. Fifty-five attendees enjoyed a tour of the USNO facilities, were able to see the moon and a dual-star and tour the USNO Master Clock facility. Currently, there are two acting officers: Jim Doherty, acting chair, and Mike Sweik, acting secretary and treasurer. A nominating committee was appointed to recommend a slate of officers by mid-June and to name an acting programs chair. The next meeting is tentatively planned for early August 2001.
DAYTON SECTION. This past year the ION Dayton Section held eight luncheon meetings that featured speakers on topics of interest to both ION members and guests. Most meetings were held at the Officer’s Club at Wright-Patterson AFB, Ohio, and were attended by an average of twenty people. The section will end the year with a late June dinner meeting at the Wright-Patterson AFB Officer’s Club, in which members and guests will participate in a social and a putting contest, and members will elect officers for 2001-2002. The Dayton Section sponsored two "Navigation Research Excellence Awards" this past year: one for an outstanding AFIT master’s thesis and one for a high school science project.
THE ALBERTA SECTION hosted five meetings since September with an attendance of between 28 to 48 members per meetings. Speakers included Amin Kassam, BC Government; A.J. Van Dierendonck, AJ Systems; Richard Andrews, Leica; Alex Bruton and Kyle O’Keefe, Univ. of Calgary; Vicki Brilz, Dynastream and the 2001 section chair, Gerard Lachapelle, University of Calgary.
THE SOUTHERN CALIFORNIA LOS ANGELES SECTION has been fortunate to have several well-attended luncheon meetings, including one on May 23 that featured Mike Full of NIMA who discussed basic Geodesy and its historical interest. Per Enge gave an interesting presentation on Air Navigation with GPS in Alaska and some initial measurements and interference work on Ultra Wide Band technologies, which no doubt will have a significant impact on the future of GPS. Kanwar Chadha, founder and vice president of marketing at SiRF Technology Inc., presented "GPS as a Location Function in Consumer Mobile Platforms: Challenges and Opportunities" - a fascinating look into the marketing of high technology consumer products. On a finanicial note, section treasurer, Ray DiEsposti, reported that section funds have almost doubled from its original seed funding. Section elections are planned for June.
SAN DIEGO SECTION. The first technical meeting of the newly resurrected San Diego Section is scheduled for late June at the SPAWAR System Center, Bayside. Chas. Falchetti will discuss experiments of using JTIDS (Joint Tactical Information Distribution System) to assist GPS receivers during the acquisition phase.
THE NEW MEXICO SECTION was very active in supporting the CIGTF portion of the June ION Conference.
THE ION ROCKY MOUNTAIN SECTION had activities in three major areas: technical meetings, youth outreach and Air Force support. Technical meetings included a talk by A.J Van Dierendonck of AJ Systems on the future GPS signals including the L5, new civil signal, and M-code. The meeting included the election of new officers: Dick Pache, chairman, and Lt. Stephen Bolt and, treasurer. Lt. Col. Daniel Jordan, the GPS commander at Schriever AFB, gave a briefing on the current status of the GPS System and answered questions posed by the audience. An El Paso Search and Rescue representative spoke about GPS applications in their work, which emphasized how essential GPS is to their mission.
The youth outreach program, started by John Lavrakas several years ago, continues with the addition of several Garman GPS units, which are in use in middle school gifted and talented classes. ION members Garth Powell, Ted Driver and Pat Sharrett spearheaded this effort. The Rocky Mountain ION section has been sponsoring a social get together for the Air Force GPS Performance Analysis Working Group meeting for the past several years, which gives Air Force types an opportunity to meet industry players in a social setting. The section also continues to present its annual ION Air Force Academy Cadet Award. The Rocky Mountain Web site (www.rms-ion.org) has been upgraded and is being maintained by ION member and former section chair, Ted Driver.
RTCA Corner
Special Committee-159 Global Positioning System Report
The fifty-fifth meeting of Special Committee-159 (SC-159) was held on May 18 at the RTCA. The reports of select RTCA Working Groups follow.
Next Meeting: Aug. 27-30, 2001
Chairman: Larry Chesto, Consultant
Vice Chairman: George Ligler, PMEI
Secretary: Young Lee, MITRE
Program Director: Harold Moses, RTCA Inc.
Working Group-1, Third Civil Frequency, continues work on GPS L5, L1 signal specification, GPS modernization and civil aviation requirements for GPS III. A new issue under study is the effect of high power M-code to GPS operation at L1.
Working Group-2, GPS/WAAS, resolved the few remaining issues concerning the new DO-229C, which will be distributed in June for committee review/approval in August.
Working Group-2A, GPS/GLONASS, continues work to determine if DO-229 should be updated to include GLONASS. The status report noted that constellation maintenance is a problem.
Working Group-2C, GPS/Inertial, completed work on Appendix R to DO-229 with selective availability (SA) and inertial reference system. A new Table R-2 was presented and approved by the plenary session and will be included for the DO-229C final review. A future update without SA depends on a revised GPS Signal-in-Space Signal Specification.
Working Group-4, GPS/LAAS, addressed CAT II/III and revisions to DO-246A and DO-253. No date was set for CAT II/III update. DO-246A and DO-253 revisions will be distributed in early July for final review/approval in August. Changes include harmonization with Standards and Recommended Practices, differential positioning service for area navigation and changes in LAAS siting constraints.
Working Group-5, Airport Surface Surveillance, continues to monitor ICAO work, DFW test program, NASA and Safe Flight 21 - key areas for GPS requirements.
Working Group-6, GPS/Interference, remains focused on the interference report on L5 and an update of DO-235. The date for the report is now March 2002 due to workload on UWB and new L5 material.
RTCA, Inc. is a private, not-for-profit corporation that develops consensus-based recommendations regarding communications, navigation, surveillance and air traffic management (CNS/ATM) system issues. RTCA functions as a federal advisory committee. Its recommendations are used by the Federal Aviation Administration (FAA) as the basis for policy, program and regulatory decisions, and by the private sector as the basis for development, investment and other business decisions.
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Corporate Profile
The Aerospace Corporation The Aerospace Corporation is a private, nonprofit corporation created in 1960 under the laws of the state of California. The purposes of the corporation are exclusively scientific: to provide research, development, and advisory services. Aerospace operates a Federally Funded Research and Development Center (FFRDC) for the Department of Defense (DOD). The corporation’s primary customer is the Space and Missile Systems Center (SMC) of Air Force Materiel Command, although work is performed for other agencies, international organizations and governments in the national interest.
From its inception, Aerospace has focused on the government’s need to develop the best space-related hardware at the lowest prudent cost. Its involvement reduces the risk of launch failure and increases on-orbit satellite endurance. Participation in each program phase - from requirements definition to launch and eventual on-orbit operation - ensures
mission success at reasonable cost. Most of the corporation’s work is hands-on engineering associated with the design, test, evaluation and initial operation of space systems.
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CALENDAR
SEPTEMBER 2001
11-14: ION GPS 2001
OCTOBER 2001
NOVEMBER 2001
JANUARY 2002 |
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