[IGSMAIL-2071] Rogue Ionosphere Problem
T.A.
T.A.
Tue Nov 17 12:13:55 PST 1998
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IGS Electronic Mail Tue Nov 17 12:13:55 PST 1998 Message Number 2071
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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 <tim.springer at aiub.unibe.ch>]
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