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Date: Tue, 17 Nov 1998 12:13:56 -0800
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Subject: No 2071: Rogue Ionosphere Problem
Status: RO
******************************************************************************
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 ]
From jfz@cobra.jpl.nasa.gov Mon Nov 16 00:15:14 EST 1998
Received: from sideshow.jpl.nasa.gov (jfz@sideshow.jpl.nasa.gov [137.78.60.30])
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(1.37.109.16/16.2) id AA284093270; Sun, 15 Nov 1998 21:14:30 -0800
Date: Sun, 15 Nov 1998 21:14:30 -0800
To: awm@sideshow.jpl.nasa.gov, dstowers@sideshow.jpl.nasa.gov,
jfz@sideshow.jpl.nasa.gov, jimr@maia.usno.navy.mil, kouba@geod.emr.ca,
larry.young@jpl.nasa.gov, mmw@sideshow.jpl.nasa.gov,
mrm@sideshow.jpl.nasa.gov, ren@sideshow.jpl.nasa.gov,
rothacher@aiub.unibe.ch, rxk@sideshow.jpl.nasa.gov,
springer@aiub.unibe.ch, stefan.schaer@aiub.unibe.ch,
tonym@sideshow.jpl.nasa.gov, ujl@sideshow.jpl.nasa.gov
Subject: TurboRogue Ionosphere Problem
Status: RO
To: Tim Springer, Markus Rothacher
>From: Jim Zumberge
Date: November 15, 1998
Re: TurboRogue Tracking
cc: Razmik Khachikyan
Jan Kouba
Ulf Lindqwister
Tony Mannucci
Marty Marcin
Angelyn Moore
Ruth Neilan
Jim Ray
Stefan Schaer
David Stowers
Mike Watkins
Larry Young
Dear Tim and Markus,
Thank you for your thorough investigation of the symptoms that, I
understand, were reported at the recent IGS Network Workshop. We have
been performing a similar investigation.
I agree with your conclusion. As I mentioned to Tony Mannucci in an
e-mail on Friday, I think the gradual deterioration in IGSnet `quality'
for low latitude sites (see http://igscb.jpl.nasa.gov/igsnet/asc1.gif
and similar plots for other equatorial sites) is probably explained by
tracking difficulties correlated with increased ionosphere activity over
the last few months. Your correlation of tracking problems with local
time is, I think, a clear indictment of the ionosphere.
> - How do other receivers perform under these conditions?
There may be some information shortly on Benchmark performance at low
latitudes.
> - Is there any possibility to fix the TurboRogue problem (software)?
We may be seeing a fundamental limit on the TurboRogue hardware
technology. We will investigate further.
> - Can all these receivers be replaced/upgraded in a timely manner?
The Global GPS Network Element at JPL is nearly done with its evaluation
of Benchmark, Ashtech, and Leica receivers. We expect to receive our
FY99 funding within weeks, at which point we'll know what sort of money
we have for receiver purchases.
(I wonder if our ionosphere colleagues could make a prediction on when
various TurboRogue receivers in the network will be reduced to, say, 2/3
of normal tracking, based on some model of how ionosphere activity will
increase over the next several months as a function of latitude.)
I can assure you that we are considering how, when, and where we can
upgrade NASA's contribution to the IGS network so as to minimize as much
as is practical these effects.
Sincerely,
Jim Zumberge
From kouba@geod.nrcan.gc.ca Mon Nov 16 02:04:51 EST 1998
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(1.38.193.4/16.2) id AA19456; Mon, 16 Nov 1998 07:04:08 GMT
From: Jan Kouba
Subject: Re: TurboRogue Ionosphere Problem
To: jfz@cobra.jpl.nasa.gov
Date: Mon, 16 Nov 1998 07:04:07 +0000 (UTC)
Cc: awm@sideshow.jpl.nasa.gov, dstowers@sideshow.jpl.nasa.gov,
jfz@sideshow.jpl.nasa.gov, jimr@maia.usno.navy.mil,
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ren@sideshow.jpl.nasa.gov, rothacher@aiub.unibe.ch,
rxk@sideshow.jpl.nasa.gov, springer@aiub.unibe.ch,
stefan.schaer@aiub.unibe.ch, tonym@sideshow.jpl.nasa.gov,
ujl@sideshow.jpl.nasa.gov
In-Reply-To: from "jfz@cobra.jpl.nasa.gov" at Nov 15, 98 09:14:30 pm
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Status: RO
Dear Jim et al.,
After the problem was reported in Annapolis, it occured to me that the
problem may be similar to early Rogues that did not work up North, due to
ionosphere. Then, If I remember correctly, the problem was with internal
smoothing within the receiver, and that sigma limits were set rather low,
typical for California ionosheric variations.
Talk to NRCan people and they confirmed to me that at least at YELL,
when receiver is smoothing phase it may lose data (due to ionosphere),
however when 1 or 2 sec sampling is on (no smoothing) the receiver is doing
fine.
So conclusion may be that a smoothing parameter sigma, set for too low
ionosphere (at least for Low lat ) may be causing it.
Second conclusion may be that bypassing the smoothing (collecting 1 s and
decimating data to 30s) may be a temproray way out of this problem.
In Annapolis, I believe this was mentioned to AOA as well as to ESA
people who raised this issue there.
Hope this helps
Jan
--
Jan Kouba
Geodetic Survey of Canada
Ottawa, Ontario, Canada
Internet: kouba@geod.emr.ca
From jimr Mon Nov 16 11:58:28 EST 1998
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From: Jim Ray (USNO 202-762-1444)
Message-Id: <199811161658.LAA28907@maia.usno.navy.mil>
Subject: Re: TurboRogue Ionosphere Problem
To: jfz@cobra.jpl.nasa.gov
Date: Mon, 16 Nov 1998 11:58:26 EST
Cc: awm@sideshow.jpl.nasa.gov, dstowers@sideshow.jpl.nasa.gov,
jfz@sideshow.jpl.nasa.gov, kouba@geod.emr.ca, larry.young@jpl.nasa.gov,
mmw@sideshow.jpl.nasa.gov, mrm@sideshow.jpl.nasa.gov,
ren@sideshow.jpl.nasa.gov, rothacher@aiub.unibe.ch,
rxk@sideshow.jpl.nasa.gov, springer@aiub.unibe.ch,
stefan.schaer@aiub.unibe.ch, tonym@sideshow.jpl.nasa.gov,
ujl@sideshow.jpl.nasa.gov, jimr@maia.usno.navy.mil
In-Reply-To: <199811160515.AAA09930@maia.usno.navy.mil>; from "jfz@cobra.jpl.nasa.gov" at Nov 15, 98 9:14 pm
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Status: RO
>
> The Global GPS Network Element at JPL is nearly done with its evaluation
> of Benchmark, Ashtech, and Leica receivers.
>
Dear Jim et al.,
Thanks greatly for the very helpful information. It would be extremely
useful if your evaluation report (or at least a summary) can be made
available to groups outside of JPL. I could see how this could possibly
cause some problems but I would hope there is some way around them.
As you know, AOA is offering a retrofit package for TRs to make them
perform essentially as Benchmarks. This is potentially a very
attractive deal but only if the upgrade fixes known problems and does
not introduce new ones. So your evaluation report would be invaluable
for making any decisions about this retrofit offer.
Thanks again,
--Jim
From igscb@igscb.jpl.nasa.gov Thu Nov 19 05:51:59 EST 1998
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(1.39.111.2/16.2) id AA276899575; Thu, 19 Nov 1998 01:59:35 -0800
Date: Thu, 19 Nov 1998 01:59:35 -0800
To: IGS Mail Recipients
From: IGS Mail Service
Reply-To: IGS Mail Administrator
Errors-To: IGS Mail Administrator
Sender: IGS Mail Administrator
Subject: No 2073: Re: Rogue Ionosphere Problem
Status: RO
******************************************************************************
IGS Electronic Mail Thu Nov 19 1:59:34 PST 1998 Message Number 2073
******************************************************************************
Author: L. Wanninger
Subject: Re: Rogue Ionosphere Problem
Dear Colleagues,
In IGS Message 2071 Tim Springer and Markus Rothacher described TurboRogue
data loss due to the current ionospheric conditions.
A closer look at some of the data files of equatorial stations from
November 8, 1998 (DoY 312) reveals that in the equatorial region the
vertical Total Electron Content (TEC) reached a maximum of around
80 TEC units (TECU) and that no small-scale ionospheric disturbances
occurred on this day. Due to the equatorial anomalies the maximum rate
of change of slant TEC exceeded the high value of 5 TECU/minute for
some low elevated GPS satellites.
In general, this kind of ionospheric condition does not cause any tracking
difficulties of geodetic or navigation GPS receivers. Therefore, it can
be assumed that the observed data loss is really a problem of a
specific receiver (or firmware) version.
Some RINEX-converters or software packages misinterpret a high rate
of change of slant TEC as cycle slips. Since the rate of change of slant
TEC under the current ionospheric conditions in the equatorial region can
exceed a carelessly selected cycle slip detection threshold for a long
period of time (hours), all observations are cycle slip flagged and finally
disregarded.
The "real" ionospheric difficulties caused by severe small-scale ionospheric
disturbances which affect the GPS-receiver signal tracking ability have not
been reported yet in this solar cycle. They are still ahead of us and will
be most severe in the equatorial region between local sun set and local
midnight. Their occurrence has a distinct seasonal/longitudinal
dependence.
[Mailed From: Lambert Wanninger ]
From igscb@igscb.jpl.nasa.gov Thu Nov 19 20:30:49 EST 1998
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(1.39.111.2/16.2) id AA045233206; Thu, 19 Nov 1998 16:53:26 -0800
Date: Thu, 19 Nov 1998 16:53:26 -0800
To: IGS Mail Recipients
From: IGS Mail Service
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Subject: No 2075: Equatorial Receiver Performance
Status: RO
******************************************************************************
IGS Electronic Mail Thu Nov 19 16:53:26 PST 1998 Message Number 2075
******************************************************************************
Author: J F Zumberge
Subject: Equatorial Receiver Performance
We acknowledge Carlos Garcia for raising at the recent IGS Network
Workshop the issue of low-latitude IGS receiver performance, and Tim
Springer for his follow-up IGSmail 2071 with more details.
We are investigating the symptoms further to determine our options in
mitigating these problems. Please be assured that we are considering
how, when, and where we can upgrade NASA's contribution to the IGS
network so as to minimize or eliminate their impact.
Sincerely,
Jim Zumberge
[Mailed From: jfz@cobra.jpl.nasa.gov]
From igscb@igscb.jpl.nasa.gov Thu Nov 19 21:18:07 EST 1998
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(1.39.111.2/16.2) id AA048015786; Thu, 19 Nov 1998 17:36:26 -0800
Date: Thu, 19 Nov 1998 17:36:26 -0800
To: IGS Mail Recipients
From: IGS Mail Service
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Subject: No 2076: Re: Rogue Ionosphere Problem
Status: RO
******************************************************************************
IGS Electronic Mail Thu Nov 19 17:36:26 PST 1998 Message Number 2076
******************************************************************************
Author: Angelyn Moore
Subject: Re: Rogue Ionosphere Problem
Dear Colleages,
In regards to the TurboRogue tracking issue, please be aware that I
have been in contact with personnel from several of the GPS-related
groups at JPL, including the Global Network Group, Ionosphere Group,
and Receiver Development Group today. Tracking under these conditions
is being actively studied in several ways by these people as well as
myself, and it is hoped that these analyses will be available soon in
order to guide a recommended course of action.
Sincerely,
Angie
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Angelyn W. Moore, Ph.D. Deputy Director, IGS Central Bureau
JPL/Caltech Angelyn.W.Moore@jpl.nasa.gov
4800 Oak Grove Dr. MS 238-540 voice: +1 818 354 5434
Pasadena CA 91109 USA http://igscb.jpl.nasa.gov fax: +1 818 393 6686
[Mailed From: "Angelyn W. Moore" ]
From igscb@igscb.jpl.nasa.gov Thu Mar 4 20:52:08 EST 1999
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(1.39.111.2/16.2) id AA255786337; Thu, 4 Mar 1999 17:12:17 -0800
Date: Thu, 4 Mar 1999 17:12:17 -0800
To: IGS Mail Recipients
From: IGS Mail Service
Reply-To: IGS Mail Administrator
Errors-To: IGS Mail Administrator
Sender: IGS Mail Administrator
Subject: No 2190: TurboRogue L2 tracking update
Status: RO
******************************************************************************
IGS Electronic Mail Thu Mar 4 17:12:16 PST 1999 Message Number 2190
******************************************************************************
Author: J F Zumberge, H J Kunze
Subject: TurboRogue L2 tracking update
Over the last three months some progress has been made on what's causing
the loss of L2 tracking in a TurboRogue (TR) receiver running at 30 sec.
(For reference, see IGSmail numbers 2071 and 2075.)
The symptom is that, when running at 30 sec in cross correlation mode
(normal for TRs when AS is on), tracking on L2 stops when the value of
P2 - P1 (actually, P2 - C/A) exceeds 12 m. (A related symptom is that,
for 8 m < P2 - C/A < 12 m, the value of P2 - C/A is quantized.)
Because P2 - C/A is essentially a measure of the ionosphere, these
symptoms are most evident in low-latitude sites. ASC1 (Ascension
Island, about -8 deg latitude) exhibits these symptoms in the extreme,
and MKEA (Mauna Kea, about +20 deg latitude) to a much lesser, but still
noticeable, extent.
When running at a 1-sec rate, the TR does _not_ exhibit the symptoms.
Limited resources have been available to examine the TurboRogue receiver
code. Some of the symptoms are understood, and some very recent
findings look promising. In fact, this week we have begun tests at MKEA
with modified firmware. At this point we are cautiously optimistic
because (i) the quantization symptom has gone away and (ii) the number
of low L2 SNR events has decreased significantly (compared, for example,
to nearby KOKB, where these events continue to occur in large numbers
near local noon).
We will be looking at precise analysis of the 1-day data over the next
several days. An initial test with the new firmware in a receiver at
JPL showed good results from such data. Nevertheless, we need several
additional days of testing at MKEA before we are confident that we've
found a firmware mod to solve this problem. At this point we expect to
have a firmware upgrade that solves the L2 tracking problem along with
the GPS week-1024 and Y2K rollover problems.
Independently, we have run the receiver at Mauna Kea at 1 sec during
much of January, and developed a perl script to mimic the TR's formation
of a 30-sec data set. Analyses of these show performance similar to
what is typically achieved with normal TR IGS data. We have also run
the ASC1 receiver at 1-sec data interval for two days, and are looking
at those results now. In the event that the firmware mod does not solve
the problem, we expect to be in a position to operate some of our
low-latitude TR receivers at the 1-sec data rate. An external PC at the
site will periodically offload the data and form the standard 30-sec IGS
product.
Of course, we should recognize that the TRs represent mature technology.
Operators of IGS sites with TRs should consider replacing them with more
modern technology, as budgets permit.
Sincerely,
J F Zumberge, Jet Propulsion Laboratory
H J Kunze, Allen Osborne Associates Inc.
[Mailed From: jfz@cobra.jpl.nasa.gov]
From igscb@igscb.jpl.nasa.gov Fri Apr 16 01:39:26 EDT 1999
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(1.39.111.2/16.2) id AA254099063; Thu, 15 Apr 1999 22:04:23 -0700
Date: Thu, 15 Apr 1999 22:04:23 -0700
To: IGS Mail Recipients
From: IGS Mail Service
Reply-To: IGS Mail Administrator
Errors-To: IGS Mail Administrator
Sender: IGS Mail Administrator
Subject: No 2240: Turbo Rogue L2 tracking problems in mid-latitude stations.
Status: RO
******************************************************************************
IGS Electronic Mail Thu Apr 15 22:04:22 PDT 1999 Message Number 2240
******************************************************************************
Author: Rene Warnant
Subject: Turbo Rogue L2 tracking problems in mid-latitude stations.
Recently, several igsmails concerning Turbo Rogue L2 tracking problems
have been posted (igsmails 2071, 2075, 2190) : these mails have reported
important data loss on L2 in stations located in the vicinity of the
magnetic equator where the ionospheric Total Electron Content is
becoming very high with the increasing solar activity.
The origin of the problem is explained in igsmail 2190 : when the
receiver is working at a 30s sampling rate under AS, tracking on L2
stops when the difference P2-P1 (or more exactly P2-C/A) exceeds 12 m.
In addition, when 8 m < P2-P1 < 12 m, the difference P2-P1 is quantized.
In fact,
P2-P1 = 0.105 (TEC/cos(Z)) + hardware biases + noise
where TEC is the vertical Total Electron Content in TEC Units (TECU)
Z is the satellite zenith angle
in most of the cases, the receiver and satellite hardware biases do not
change much with time; for this reason, we can consider that P2-P1 is a
measure of the TEC. This explains why the L2 tracking problems have been
detected in stations where where the TEC is very high.
Our station of Brussels (Belgium, Europe, lat 51° N) is a mid-latitude
station where the ionosphere is "quiet" when compared to equatorial
stations. Since the second part of the year 1998, the TEC observed at
Brussels is increasing. The maximum value we have observed (in November
98) is 50 TECU and we regularly observe values between 30- 40 TECU. When
I read igsmail 2190, I computed if these TEC values could give P2-P1 >12
m. THE ANSWER IS YES !!! I give you some examples:
if TEC = 30 TECU ===> P2-P1 >12 m for elevation angles below about 15°
if TEC = 40 TECU ===> P2-P1 >12 m for elevation angles below about 20°
if TEC = 50 TECU ===> P2-P1 >12 m for elevation angles below about 25°
This has been confirmed when having a look to our data files ! I have
observed an important data loss at "low" elevation. This means that the
L2 tracking problem is a reality for every IGS site working with a Turbo
Rogue receiver.
The solar maximum is foreseen for the begining of year 2000; it is clear
that we can expect to reach values of 60 - 70 TECU and higher even in
mid-latitude "quiet" stations as it has been the case during the
previous solar cycle.
A solution to this problem consists in observing at 1 sec sampling rate.
Unfortunately, in this case the measurement noise of all observables
increases significantly. This is due to the fact that when observing
with a sampling rate of 10 s or more, the receiver makes an internal
smoothing of the data; it is not the case with a sampling rate lower
than 10 s. This increase of the measurement noise can give some problems
with processing softwares.
IGS station managers should be aware of these problems and have a look
to their data.
Rene Warnant.
--
***********************************************************
Dr. Rene WARNANT Tel: +32-2-373 02 51
Royal Observatory of Belgium Fax: +32-2-374 98 22
Avenue Circulaire, 3
B-1180 BRUSSELS
Belgium
e-mail: R.Warnant@oma.be
http://www.oma.be/KSB-ORB/D1/GPS/main.html
***********************************************************
[Mailed From: Rene Warnant ]
From igscb@igscb.jpl.nasa.gov Mon Apr 19 16:49:11 EDT 1999
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(1.39.111.2/16.2) id AA190441756; Mon, 19 Apr 1999 12:55:56 -0700
Date: Mon, 19 Apr 1999 12:55:56 -0700
To: IGS Mail Recipients
From: IGS Mail Service
Reply-To: IGS Mail Administrator
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Sender: IGS Mail Administrator
Subject: No 2241: TurboRogue L2 tracking update
Status: RO
******************************************************************************
IGS Electronic Mail Mon Apr 19 12:55:55 PDT 1999 Message Number 2241
******************************************************************************
Author: JPL GGN Element
Subject: TurboRogue L2 tracking update
IGSmail #2240 quantifies the relations among elevation angle, TEC, and
the TurboRogue (TR) L2 tracking problem. We, too, have observed the
symptoms at a mid-latitude receiver (JPL, 34 deg lat), for data at
low-enough elevation angle. We agree with Rene Warnant that the problem
is either already present or potentially present in all TRs.
Since our last update on the status of our working this problem (IGSmail
2190, March 4, 1999), there has been additional progress. We do not yet
have a TR software solution (we _are_ getting closer...).
We _do_ expect the alternate workaround -- operate the TR at 1 s,
offload these data locally, form a 30-s IGS product -- to be installed
at our site in Bogota, Colombia (bogt) before the end of this month.
[Mailed From: James F Zumberge ]