From T.A. Tue Nov 17 12:13:55 1998 From: T.A. (T.A.) Date: Tue, 17 Nov 1998 12:13:55 PST Subject: [IGSMAIL-2071] Rogue Ionosphere Problem Message-ID: ****************************************************************************** IGS Electronic Mail Tue Nov 17 12:13:55 PST 1998 Message Number 2071 ****************************************************************************** Author: T.A. Springer Subject: Rogue Ionosphere Problem Dear Colleagues, Below in Figure 1, we show a pseudo graphics of several RINEX files for November 8, 1998 (day of year 312). In this graphic each 20 minute interval of the RINEX file is summarized using one-character. This character indicates the number of observed satellites in a 20 minute period. A "-" means that less than 4 satellites were observed whereas a " " (blank) means that no satellites were observed (no data). Finally a "*" means that more than 9 satellites were observed. In Figure 1 below we show the equatorial stations sorted by longitude, starting in the east with the station KWJ1 and ending in the west with the stations on Hawaii (KOKB, MKEA) (east and west relative to Europe). On first sight it is obvious that the data quality is very bad. If we look more carefully we can see that the period of bad tracking is moving in time when the stations are sorted by longitude. The bad period being roughly around local noon. We are therefore convinced that the bad tracking performance of the stations is caused by the ionosphere. ---> This means that we have a very serious problem in the IGS ! The mean TEC (total electron content, which is a measure for the ionospheric activity) is currently still at a very mild level of about 30. Over the next 3-5 years, as we are moving towards a new solar maximum, this level will increase significantly (mean TEC of 50-60)! This means that, with the receiver performance as indicated in Figure 1, we will loose a lot of data. Probably all data from stations around the (geomagnetic) equator will by lost but also the higher latitudes will suffer as we move towards the solar maximum. If you are not convinced by just one day please also look at Figure 2 which shows some of the problems over the last 12 days. Also take a look at Table 1 which shows the effect of the bad tracking on the repeatability of the station coordinate estimates. For comparison it also gives the mean repeatability over all our 100+ stations (for week 982). You will note that the repeatabilities for the equatorial sites are up to 5 times larger than the average repeatability! Furthermore, we would like to point out that all stations in Figure 1 are equipped with a TurboRogue receiver except the station BAHR which uses an Ashtech-Z12. It can clearly be seen that BAHR shows perfectly normal tracking performance (remember that "*" means more than 9 satellites tracked). Notice that BAHR has the same latitude as e.g. LHAS and MAS1. So clearly this Ashtech receiver has no problems with the current ionospheric activity. Unfortunately we have only two Ashtech receivers in the equatorial band, BARB and BAHR, and no other receivers. Because we have not received any data from BARB recently it does not show up here. However, we checked BARB for the period of day 260-270 and compared it to the stations CRO1 (north of BARB) and KOUR (south of BARB). Both CRO1 and KOUR show significant tracking problems around local noon for this period whereas no degradation can be seen for BARB. Conclusions: ------------ We conclude that all types of TurboRogue receivers experience severe tracking problems under the current ionospheric conditions, which are still comparatively mild. With all types we mean the SNR-8000, SNR-8100 and also the SNR-12 RM. Of course some of the problems in Figures 1 and 2 may be site/set-up dependent but it is clear that a major part is induced by the ionospheric activity. Secondly, we conclude that it is very likely that the Ashtech-Z12 does not suffer from this problem. Because we have only two of these receivers in the equatorial band, we cannot tell for sure, but the evidence provided by these two stations is very convincing. The big question now is: WHAT CAN BE DONE ABOUT THIS ? Some other important questions which we will have to answer soon are: - How do other receivers perform under these conditions? The Ashtech seems to be OK, what about Trimble and Leica, and possibly the new Rogue (benchmark). Does anyone currently operate such receivers within 15 to 20 degrees of the (geomagnetic) equator? - Is there any possibility to fix the TurboRogue problem (software)? It has been reported several times over the last couple of years that there are problems with (Turbo)Rogue receivers in case of high ionospheric activity, e.g. the station YELL has shown problems several times over the last couple of years (where we had minimal ionospheric activity). Is this a software problem which may be fixed or is it a hardware problem? Why is it happening? - Can all these receivers be replaced/upgraded in a timely manner? The ionospheric activity is increasing rapidly. This means that soon we will loose most of the data in the equatorial band. This will have a severe impact on the IGS products (not to mention the ionospheric pilot project). If the problem cannot be fixed it will be mandatory to replace many of the TurboRogue receivers, especially in the equatorial band. But as the ionospheric activity increases the latitude band will increase significantly. How far the critical latitude will extend is unclear right now but if we assume that it increases linearly with increasing ionospheric activity this problem might affect stations at a latitude of up to 40 degrees (North and South). We sincerely hope that this problem can be solved very soon! Kind regards, Tim Springer Markus Rothacher The CODE Analysis Center ps. This problem was also brought up at the recent IGS Network Systems Workshop by Carlos Garcia from ESOC/ESA. ps. Some very preliminary results from Roman Galas at GFZ indicate that the new AOA receiver (called benchmark) seems to be alright. ps. Please excuse us for this rather lengthy e-mail but we felt that this is a very important issue. Figure 1: RINEX GRAPHIC FOR DAY 312, 1998, EQUATORIAL STATIONS BY LONGITUDE ------------------------------------------------------------------------------ PHASE OBSERVATIONS BOTH FREQUENCIES KWJ1 |----------------------44-44444576665657656766775577668766766544444444--- GUAM |- ----- --------------------444454455665456764-5-44445775566566666-- WUHN |-54444544-454555--4444-------4444555577765556756777556678778777566676675 XIAN |--54456555566576664444544----5465555676776566754776756676678876777755667 NTUS |---------------- -- - -- - -------------57876575766776668677886665877 LHAS |445654454444--44------ -----4555666677776768667666665445555----45554 IISC |676767767776444-------------------------4445566666666577887545454555546- DGAR |7776554-------------- ------------445455777566765777566776777767 BAHR |89899*****999*9888789787877879****99898898889988988888**9889899999989777 MALI |67866665666655-445-------------------44----4456654--55456764566667667564 MAS1 |444655545444545455554656667655556545444------------45567676654-544444-44 ASC1 |5564644766678747657887655554---------- -- -- - ------------4444-444-4 FORT |4-----4----4554556666887756776444------------------------ -------6544555 CRO1 |45-444--44445665545457665566544454------4-------44--4554--4-4--4-44444-5 BOGT |4------------44-5677665666656646654--------------4444------------------4 AREQ |44-555577777776688765555778755-665666557554--4-------------------------4 SANT |------44464-44-555655666667-456444-4444-4----------------------5-44----- GALA |------4-444664-5555466765-76478777766545------------- - --- ------- EISL |--444----44---4---4444-4--55577665677785665-4-4-444-------------------44 KOKB |----- -------44-44-----4-----45657655677775677866854------ ----45444455 MKEA |-------------44-4454--4--------566765656575666777776544-----445465555456 -----+-----------------+-----------------+-----------------+-----------------+ 0 12 24 Some other stations in the equatorial region which may be affected but for which no or to little data was available to tell on this particular day. -------------------------------------------------------------------------- SHAO: few data on this day KOUR: no data on this day BRAZ: no data " " " BARB: no data " " " (Ashtech-Z12) TAHI: no data " " " Table 1: Stations repeatability from CODE for GPS week 982. ---------------------------------------------- Station repeatability (mm) N E U ---------------------------------------------- GUAM 50501M002 7 NNNNNNN 2.9 4.4 19.4 IISC 22306M002 7 MMMMMMM 4.7 5.1 12.5 ASC1 30602M001 7 MMMMMMM 2.9 12.4 24.8 GALA 42005M001 7 MMMMMMM 4.4 10.3 9.4 BOGT 41901M001 7 MMMMMMM 4.1 1.8 19.0 DGAR 30802M001 5 MMMMM 5.5 15.8 28.3 ---------------------------------------------- MEAN OVER ALL 113 STATIONS 1.9 3.2 5.9 ---------------------------------------------- Figure 2: RINEX GRAPHIC FOR DAYs 300-312, EQUATORIAL STATIONS BY LONGITUDE -------------------------------------------------------------------------------- kwj1 301 |4--------4---4--44345567655455655786546675557767766667687777756666654444 303 |54----------------555667654555756776457666777567765-76786568777766554444 305 |4-------------4445444577744467767855576765666567556776786667655455------ 306 |44---------------5545555453556656766465655677566557776877787755556544444 307 |--------------------4-65444557577655565765676566557766877766564444434553 308 |4----------------5456665535557577655665666776566557776876677654455544553 309 |----------------------5544555656776577664567656656776787858754444--44--- 310 |--------------------4355435657577555657656775665567767877776554454------ 311 |----------------------5534456757775555665776566557776877777655554------- 312 |----------------------44344444576665657656766775577668766766544444444--- guam 300 |6--44-------4---------4----566677544455544566656666643565545576556566666 301 |5--------------------------444444544455445566655676634454455- -56676666 302 |4--4---------------45567555566677654455445676655576435554455775556667665 303 |4---4----4---4-------------466-77544455445566566676455544556775666666666 304 |4--------------------4---43555566544455446566655566435544555765666676666 305 |4--------------------------556555544554446666455666425644455765665666666 306 |---------------------------444655444554446666556765344544556765567666666 307 |34-------------------------555665444554445665556764454544657755666766653 308 |---------------------------4445454445545456655667644454454677565666666-- 309 |---------------------------4445444445544454666666534565565676576565565-- 310 |---------------------------4444434445445556655576643464455573656656665-- 311 |-------- ----------- ------444354444544455554555434455556677656654554--- 312 |- ----- --------------------44445445566545676435344445775566566666-- lhas 300 |7545666667766555556654-------------------6667766565656567776575766767687 303 |6556667577665555445--------------445556764676667666577787765557666777677 308 |556667657355444444------------454555567666777666666766777655576667767775 309 |45666665765544344---------------4556567666677655565877877656576676768775 310 |556666667655454444--------------5556567656776656665677877657676666767765 311 |55666656665445444---------------4456566544645444555566776555554566656664 312 |445654454444--44------ -----4555666677776768667666665445555----45554 iisc 300 |55577566777887444-----------------4-----46676676667654666667645666855545 301 |575766677676774--4----------------------56665566668866566577755546754434 302 |56577778765674444-----------------------4675566666865555688855--47644555 303 |536766666667754-------------------------55655666667546556777575566556655 304 |6677666776676444---------------44------467666766676546666777566566545545 305 |46776667656784444-----------------------67766766688666755676555467544444 306 |768576777675---------------------------457765666686656676787465573656657 307 |86767776667644-------------------------456567766686566676775556666556667 308 |46776667556644--------------------------5655766668655556665555647--45456 310 |677667765675----------------------------45554555445555777765456766664677 311 |68676777677444--------------------------4545555676544--5554465544--66567 312 |676767767776444-------------------------44455666666665778875454545555463 dgar 300 |76766644--------------------- - ---------------44445566746767777776887 301 | -7675454555554------------ --------------55455-----44446666765567767787 302 |77787555---------------- - -- ----------4------44444456555664667777877 303 |77677555344--------------- ---------------4-----444545556577654567766777 304 |67667544--------------- -----------44444456667656777776787 305 |67877564------------------ ---------------4424--44455556545555667667878 306 |67776444--------------- - -- ----44-----------44554545676667866 307 |67776554---------------- ----------------4---44455556444655566767766 308 |6677574------------- - ---- -------------44444444554--5566667666 309 |777754----------- ---------------4544456666668786 310 |7677664--------------- - ----- ------------444355566546444776688786 311 |777744---------------- ----------------------4----456---555766677786 312 |7776554-------------- ------------445455777566765777566776777767 asc1 300 |566566665676667646767888756665555---------------------------------456644 301 |545456664776656766666888656755544--------- --------------------455555545 302 |5---655547676887576658875455444---------- -- -- - ---------------444 303 |-44566765767448567668777666654----------- ------- --------------444454-- 304 |45556662476677756765888766565434-------- -- ---- ----------4555455445 305 |455556746866667677668887566564---------- -- - - - ---------------44444 306 |4555675566674875665588776556544--------- ---------------------454444--4 307 |4557784386767876766688777664--4--------- - - -- - ---------43443 308 |4556666576778855756688766566434------ - - -- -- --- --------444553 309 |645566568667775656678866555------------- - ----------- ---------444443 310 |5453675666788756766-8876763544--------- - - - ----------4444 311 |---454--455676565577787655655------- -- - - -- -- - -----444554456 312 |5564644766678747657887655554---------- -- -- - ------------4444344434 mas1 307 |5454655555444555654554657668777776554444-------555754556557664--43454--4 310 |45465545544464556665555766877777664444--------------4--5577554--54544454 311 |44455553444444546665465766878776664544----------------455766554555544365 312 |444655545444545455554656667655556545444------------455676766543544444244 fort 300 |55545455556665786556676787865688545644445--4-4554--4----------45-5666555 301 |555554455576657875565678877656874346----4--44434---------------544566554 302 |555443555677667775566668877567875344-------44544434--------4---424776554 303 |555544555667547565567678876556865454----4444444--------44--4454434665556 306 |5544455566666777556666887- 307 |65534455677657855566668877457864454---------454------------------5655355 308 |554--555667668555567668876557873454------44---------------------4-755455 309 |5643555565755865566766877646876444------------------------------45534445 310 |544444556566775556676687865787444--------------------------------6745555 311 |554445556544564556666787765677--44----------------------------4444454--4 312 |4-----4----4554556666887756776444------------------------ -------6544555 cro1 300 |4445545344445644665556667766565545554-----44--5--544455543444--445553454 301 |34555------4545466554565777565754543453525444---566576665544434445454454 304 |465555342534566555546567776565545444--4--444----655555444543434553534544 307 |56544----4356466654555776656555465444---44--4524444445543444244555344444 308 |5555544----56465554655776656554554444---54434315443555544444344554434444 309 |54555343444555555535537766566544534534--44------454655544--4343443444444 310 |55534343444545665455656766565545543534--44--4--------454--4----4--444444 311 |54444444345543565445567755665544534434--44344---------------4434--443444 312 |453444--44445665545457665566544454------4-------44--4554--434--434444435 areq 301 |544545655731128768888755656787653457877766666665444---4-------4244434534 303 |55555655677665776888866555788754466777755666665544------------4444434544 304 |4445565587866676688885655668875346677775666765554------------44444--4545 305 |4555665587865676688875666678855345677775667655554------------44444--4544 306 |445466567675677668886557678875535777776676665554-------------4444---4555 307 |555566558777777677886656567874436677776555564554---4-----------4-----455 308 |5455555677777775888766555788654366776665656655544--------------------444 309 |44446556776657667888665567887535767776557564454-----------------------44 310 |4434555776777766888766556787653466676656756445-------------------------- 311 |4---555767777666788654557787653577676556655454---------------------- -- 312 |4435555777777766887655557787553665666557554--4-------------------------4 bogt 300 |--4-----4425645566678766656465554475456553455--555555555665554--54-6---- 301 |--44----53577556655577555555555445453454----------4----444554434434----- 302 |--4-------45767786677755566--566576556645366---46656565666555435554444-- 303 |--54------444455655876555556556656644554---------4546656555443434------- 304 |--4-------56466566487666565655544565455----------4--45445444----444----- 305 |34--------4434444--66445455666555652465-----------4- 306 | --------44455655877555665666656653454----4---555556664555444344------- 307 |44--------46455555777545666656656654554---------565455544------444------ 308 |44--------444553658754555566564466544544344----5454555645544346554------ 309 |4------43444555655875665646555446644554-------------------4------------- 310 |44--4--45554556455874555566656557645565-----------4--------------------- 311 |4--------4545555677756555565554565345-------------------4--------------- 312 |4------------4435677665666656646654--------------4444------------------4 gala 300 |25546576567766666655664577746757767666666566666666765------------------- 305 |----453456667655666754557645757777776555576443444----------------------- 306 |---45555545666666767545576467577777766556664565655---------------------- 307 |---4454566445556676666676647757777775653555----4------------------------ 308 |----4455455586666777556---5766777777666466644--------------------------- 309 |----4--44654655666765666655866777766654565------------- -- --- ------- 310 |-------5545566677665576765665776777655434------------ -- - - ------ 311 |-------44544--55667666765576577666666656654--------------------- ------- 312 |------4344466435555466765376478777766545------------- - --- ------- eisl 301 |54456545466887756766677654676667776677778776666655444------4344----44--5 305 |565655546688875- -6676557766577766577787666666544444--------4----444555 306 |5655544465887656766676654676667775667778766665645444---------4-----44455 307 |444554--45676656655654654676567765667778766666644444-------434----445455 308 |4554545565677656766667644666567765587778766666654444--------------444454 309 |45455434667867676566766457665677665777776666544--------------------45344 310 |545554556676655666666655665556776657778766655--------------------------- 311 |34444--466766555656766546756677656677786566465444----------------------4 312 |--444----44---4---444434--5557766567778566534343444-------------------44 kokb 306 |24444456556743577677666678876675677887666777658777687465544------- - 307 |-------443444445555666666886666566686666566666877667646544-------- -- 308 |-------43543445576566666687666566768666667765776776866665444---44------- 309 |--444545555434667556667676666556677866647676587776774655434---44---- --- 310 |--------434--5667566666666665546678666657676587886774655444444444434---- 311 |------43444434566666766688666755778876666776676886875644---------------- 312 |----- -------44344-----4-----45657655677775677866854------ ----45444455 -----+-----------------+-----------------+-----------------+-----------------+ 0 12 24 [Mailed From: Tim Springer ]