Subject: [IGSMAIL-2071] Rogue Ionosphere Problem
From: T.A. Springer
Date: Tue, 17 Nov 1998 12:13:55 PST

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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 <[email-masked]>]