remote sensing the ionosphere using gps-scinda dr. charles carrano 1 dr. keith groves 2 1 institute...

REMOTE SENSING THE IONOSPHERE USING GPS-SCINDA

Dr. Charles Carrano1

Dr. Keith Groves2

1Institute for Scientific Research, Boston College2Air Force Research Laboratory

IHY-AFRICA / SCINDA 2009 Workshop

Livingstone, Zambia 7-12 June 2009

What is GPS-SCINDA?

• A real-time GPS data acquisition and ionospheric analysis system for SCINDA, written in C for the LINUX operating system

• Computes ionospheric parameters S4 and TEC using the full temporal resolution of

the receiver. This high rate sampling (10-50 Hz) makes scintillation monitoring possible. Standard IGS/RINEX observations are inadequate for scintillation obs.

• Software designed for use with a number of relatively inexpensive and off the shelf receiver models (including the Ashtech Z-XII, Ashtech Z-CGRS, and the NovAtel GSV 4004B).

• Provides a real-time display of satellite tracking status and the ionospheric parameters.

• Includes a suite of scripts for automated data delivery, data management, and data backups onto CD-ROM or DVD media.

• A new configuration tool is included to assist with installation of the software and selection of data logging options.

What is WinTEC-P?

• Software for the calibration of GPS TEC measurements made using GPS-SCINDA. It is also written in C for the LINUX operating system.

• An extension of a Kalman filter approach developed at NOAA/SEC for TEC calibration called WinTEC (MS Windows). Our implementation (LINUX) includes several new features including estimation and removal of the plasmaspheric contribution to the TEC.

• It can estimate and remove instrumental biases associated with the GPS receiver and (optionally) the GPS satellites without any external information (e.g. satellite biases or almanac files), which makes it well suited for automated processing in the field

• Includes programs written in the GNU R to plot S4 and calibrated TEC. Scripts are

included to automatically generate and archive daily S4 and TEC plots with 15

minute updates.

• WinTEC-P can also be executed manually (for post-processing) on GPS datasets of arbitrary duration (to create weekly plots, etc).

What’s New with this Release?

• Previous versions of GPS-SCINDA recorded the differential GPS observables TECP and TEC but NOT the individual phases and pseudoranges. Therefore, it

is not possible to create RINEX files from old GPS-SCINDA measurements except when recording the full raw 50 Hz data (campaign mode).

• The new version of GPS-SCINDA now records the standard NovAtel RANGE records to files with the extension *.rng at a rate of 1 every 10 seconds (by default). These RANGE files may be converted to RINEX using GPS-SCINDA.

• The WinTEC-P software for TEC calibration is now integrated into the GPS data collection system. Daily plots of S4 and TEC (and also optionally the post-processed data) are updated every 15 minutes and automatically archived on the computer for convenient access.

• It is no longer necessary to download the satellite and receiver biases for your specific receiver from the SCINDA Web site.

• Data can be delivered to multiple remote sites automatically.

• All users GPS-SCINDA users are encouraged to upgrade their software.

System Components

GPS-SCINDA System Hardware

Equipment List

1: NovAtel GSV 4004B GPS receiver

2: NovAtel dual frequency antenna

3: Antenna cable (30 meter maximum)

4: Serial cable

5: Power cable

6: Personal computer running Linux

GPS-SCINDA System Software

The GPS-SCINDA data acquisition and ionospheric analysis system:

• Runs on a PC or laptop running LINUX (Debian distribution preferred)

• Displays GPS tracking and ionospheric parameters with real-time updates

• Configurable by running a configuration script and answering questions

• Sends data to one or more hosts via a secure Internet connection

Contributions to the AFRL-SCINDA Network

AFRL

NOAA/NGDC

Boston College

AFWA

GPS RX

PC

GPS-SCINDA

GPS RX

PC

GPS-SCINDA

GPS RX

PC

GPS-SCINDA

Global Data Products

Global Data Distribution

AER

Network maintenance Collaborative scientific studiesModel development, etc.

System Operation

System Operation, Part I

GPS-System Boot Menu

- Do not run

- Normal mode

- Campaign mode

User can reboot at any time to choose a new mode of operation

Default mode may also be changed by running configuration script

GPS Data Collection System for SCINDA AFRL/Radex

===================================== ==========

Choose the mode of operation (default = 2):

-------------------------------------------

1) Do not run the GPS software

--> 2) Normal mode (collect SCINDA data only)

3) Campaign mode (collect SCINDA data and raw data)

Use the up and down arrow keys to select and press enter when ready.

You have 30 seconds to make a choice.

System Operation, Part II

Satellite PRN

This screen is reached by Pressing the “Ctrl”+“Alt”+“F1” Keys at the same time

GPS Operational Display

Azimuth

Elevation

C/No of C/A code

C/No of P code on L1

C/No of P code on L2

S4 on L1

S4 on L2 (unusable)

Relative (uncalibrated) TEC

Receiver position

System status

Switching to the Linux Console

Debian GNU/Linux stable cvd-gps.bc.edu tty1

cvd-gps.bc.edu login:

Linux Console

GPS Display

Press Ctrl-Alt-F2

Press Ctrl-Alt-F1

Note: the hostname “cvd-gps” will likely be different for your computer

To log in to the Linux console: At the prompt “cvd-gps login:” type rootAt the prompt “password:” type password

Data Recorded by the System

GPS Data Collection and Storage

A collection of Perl scripts manages the delivery and archiving of the data

• New data files (less than 24 hours old) are created here:

/home/gps/data

• Files more than 24 hours old are moved to an archive directory according to the year and month. For example, data for July 2006 reside here:

/home/gps/archive/2006/07-Jul/

• Files moved to the archive are automatically compressed using the LINUX “gzip” command, which adds “.gz” to the filename (use “gunzip” to uncompress).

• Data files queued for delivery over the Internet are copied to this directory (and removed after they are sent):

/home/gps/xfer/

Types of Files Recorded

090524_150000.nvd.gz – streaming raw data (50 Hz)

090524_150000.scn.gz – ionospheric statistics (S4, TECP, TEC)

090524_150000.psn.gz – receiver position (1 Hz)090524_150000.msg.gz – diagnostic messages090524_160000.ism.gz – GSV 4004B ISM messages

090524_150000.scn.gz – ionospheric statistics (S4, TECP, TEC)

090524_150000.psn.gz – receiver position (1 Hz)090524_150000.msg.gz – diagnostic messages090524_160000.ism.gz – GSV 4004B ISM messages (60 sec)090524_150000.rng.gz – NovAtel RANGEB messages (for RINEX)

YYMMDD_hhmmss – Time tag format (UTC via PC clock)

campaign

scinda

Data collectionmode

Files recorded (hourly) Description

year month(1-12) day(1-31) hour(0-23) minute (0-59) second (0-60)

YY – 2 digit yearMM – monthDD – dayUTSEC – seconds since midnightAZ – azimuth (deg)EL – elevation (deg

L1S4 – Scintillation intensity index on L1L1S4 – Scintillation intensity index on L2 (do not use)%SAM – % samples taken compared to number expected (0-100%)

TECP – Differential pseudorange (TECU)

TEC – Differential carrier phase (TECU)

ROTI – STD of rate of change of TEC over one minuteTECR – Relative (uncalibrated) TEC (TECU)N – Time since last cycle slip (min)PRN – pseudorandom noise satellite identifier

Legend:

Format of the Ionospheric Statistics Files (*.scn)

# YY MM DD UTSECT 03 09 30 42972132.3 55.0 0.12 100 0.06 100 52.4 -1.105 0.78 38.1 74 09 52.0 38.0 0.16 100 0.09 100 23.8 13.767 1.37 35.9 76 26 57.0 20.0 0.10 100 0.03 100 52.8 5.995 0.80 60.3 16 29

. . .T 03 09 30 43032131.8 55.6 0.07 100 0.03 100 50.1 -1.106 0.65 38.3 75 09 52.0 37.5 0.13 100 0.09 100 30.6 14.071 1.18 36.1 77 26 57.0 19.3 0.10 100 0.07 100 55.6 6.526 0.81 60.5 17 29

# AZ EL L1S4 %SAM L2S4 %SAM TECP TEC ROTI TECR N PRN

1st epoch

2nd epoch

Formats of the other files are given in an appendix to these slides and also a technical report

Generating RINEX Files using GPS-SCINDA

Use this command to generate RINEX files from RANGE files using GPS-SCINDA:

./gps-scinda –r novd --interval 10000 --rinex *.rng

interval in ms(1000 ms)

This will produce hourly RINEX files. To generate daily RINEX files, concatenate the hourly *.rng files together first, and then generate RINEX from this daily file:

cat 090601_*.rng > 090601.rng

./gps-scinda –r novd --interval 10000 --rinex 090601.rng

Configuring a GPS-SCINDA System

GPS-SCINDA Software

gps-scinda-bundle.tar.gz - Archive containing all the software for SCINDA

install - Script to install (or upgrade) SCINDA softwaregps-scinda-1.76.tar.gz - GPS-SCINDA data collection software (binary version)gps-scinda-src-1.76.tar.gz - GPS-SCINDA data collection software (source code)wintec-p-1.05.tar.gz - WinTEC-P software for TEC calibration (binary version)wintec-p-src-1.05.tar.gz - WinTEC-P software for TEC calibration (source code)gps-scripts-2.00.tar.gz - Scripts for automated data management and delivery

Files Description

GPS-SCINDA component can also be used separately to post-process raw data collected previously, or to convert RANGE (*.rng) files to RINEX files.

WinTEC-P component can also be used separately to calibrate TEC measurements previously collected with GPS-SCINDA.

The latest version of the software may be downloaded from this URL:

https://wfs.bc.edu/carranoc/scinda/gps-scinda-bundle.tar.gz

Preparing a New Computer for GPS-SCINDA

Steps to prepare a new computer for GPS-SCINDA:

1) Install Debian LINUX and edit /etc/network/interfaces (if necessary) to connect the computer to the Internet

2) Add a Debian repository to /etc/apt/sources.list so you can download packages with the apt-get package manager (otherwise apt-get will look for packages on the Debian CDs)

3) Create a user account named “gps”

4) Optional: Disable automatic startup of XDM/KDM/GDM (i.e. automatic start in X Windows) or you will not see the real-time display automatically after rebooting

5) Recommended: Configure the bios to restart the computer automatically when power returns (after a power outage).

These tasks can be accomplished with the help of a systems administrator (or we can send you a preconfigured system).

unpacking the tar file gps-scripts-2.01.tar.gz starting configure.pl

--------------------------------------------------Configuring the GPS-SCINDA data acquisition system--------------------------------------------------

Enter the three letter station abbreviation [slz]:

Installing or Upgrading the SCINDA Software

Start data collection in campaign or scinda mode (campaign/scinda): [scinda]

cd /home/gps

tar xzvf /path/to/gps-scinda-bundle.tar.gz

install gps-scripts-2.01.tar.gz gps-scinda-src-1.76.tar.gz gps-scinda-1.76.tar.gz wintec-p-src-1.05.tar.gz wintec-p-1.05.tar.gz

root@hostname:/home/gps#

./install

los

Enter the GPS receiver type (uz=Ashtech uZ-CGRS, z12=Ashtech Z-XII, novd=Novatel): [novd]

Log into the computer as the root user and then do the following …

root@hostname:~#

root@hostname:/home/gps#


Shall I install prerequisite software using apt-get? This requires internet access (y/n): [y]

Enter the IP address of remote host #1 where the data will be sent: [136.167.18.134]

Enter the name of the user on 136.167.18.134 where the data will be sent: [los-gps]

DSA key /home/gps/.ssh/id_dsa.pub was found (please email this file to [email protected])

Enter the IP address of remote host #2 where the data will be sent: [66.155.158.52]Enter the name of the user on 66.155.158.52 where the data will be sent: [los-gps]

DSA key /home/gps/.ssh/id_dsa.pub was found (please email this file to [email protected])

Missing software: Looking for package openssh-server, Found openssh-server Looking for package libncurses5-dev, Found libncurses5-dev Looking for package libcurses-perl, Found libcurses-perl *** Warning: Could not find package libgsl0-dev. *** *** Warning: Could not find package r-base. *** Looking for package ntp, Found ntp

The following prerequisite packages are missing: libgsl0-dev r-base


Backing up previously installed software Installing from gps-scinda-1.76.tar.gz Installing from wintec-p-1.05.tar.gz

Checking the version of gps-scinda ... gps-scinda 1.76 is correctly installed

Checking the version of wintec-p ... wintec-p 1.05 is correctly installed

Setting the p1c1 option in wintec-p.conf according to the receiver type executing command: ./set-option.pl p1c1 1 wintec-p.conf

Record NovAtel RANGE files during data collection (may be converted to RINEX later) (y/n): [y]

Install GPS-SCINDA and WINTEC-P from (b)inary package or (s)ource code package (b/s): [b]

Record RINEX files during data collection (they require a lot of disk space) (y/n): [n]

Keep an archive of daily calibrated TEC files (they require a lot of disk space) (y/n): [n]

The NovAtel GSV4004B can track up to three SBAS signals.Shall I update the sbas.dat file (y/n): [y]Please specify your longitude sector: 1=American, 2=African, 3=Indian, 4=Pacific, or 5=Southwest Asian: [1]


Updated sbas.dat as follows: 124 126 120

Checking the timezone of software clock (GMT or equivalent is recommended)Local time zone is set to GMT or equivalent.

Configuring the NTP server (time will be slaved to this host)

Activate the GPS software: [Y]

2

The GPS system has been activated. Please reboot(type /sbin/reboot) for this change to take effect.

Installation complete. To reconfigure this system, type "./configure.pl"

root@hostname:/home/gps# /sbin/reboot

After the computer reboots, the data collection software should start automatically. This

configuration process may be repeated (i.e. if you make a mistake) by typing: ./configure.pl

Enabling Automated Data Delivery

• The recorded data is delivered over the Internet using SFTP

• By default, all data files are delivered except the raw 50 Hz data (if present) and RINEX files, since these file are too large for slow networks to handle.

• If the available bandwidth onsite is insufficient to deliver all the files, the system can be configured to omit certain types of files.

• In order to connect to our servers using SFTP, an SSH key must be generated as the “gps” user on the computer:

ssh-keygen –t dsa

• This step is performed automatically (and only once) by the install script. We have already performed this step on computers we have configured for you.

• The SSH key file /home/gps/.ssh/id_dsa.pub which is generated in this step should be emailed to us as an attachment so we can install it on our systems.

How S4 and Absolute TEC are Computed

The Scintillation Intensity Index, S4

• A statistical measure of the intensity of amplitude scintillations is given by the scintillation intensity index, S4

• May be interpreted as the fractional fluctuation of the signal due to ionospheric modulation (e.g. S4=1.0 means 100% modulation)

• We typically use the C/No (converted to linear units) as a proxy for the signal intensity, although this isn’t strictly correct.

• We use the maximum data rate available (10, 20, or 50 Hz, depending on the receiver model) to calculate the S4.

• In addition to the normal GPS satellites, we can compute the S4 along the link to geostationary SBAS satellites which broadcast on L1 only

I

IIS

22

4

Signal intensity standard deviation

Signal intensity mean

Monitoring SBAS Satellite Links

SBAS Satellite Longitude

Galaxy 15 (WAAS/PRN 135) 133.0º W

Anik F1R (WAAS/PRN 138) 107.3º W

AOR-E (EGNOS/PRN 120) 15.4º W

ARTEMIS (EGNOS/PRN 124) 21.6º E

IOR-W (EGNOS/PRN 126) 24.8º E

MSAT-1R (MSAS/PRN 129) 140.1º E

MTSAT-2 (MSAS/PRN 137) 145.0º E

Highest elevation SBAS satellites from African Sector are PRNS 124, 126, 120

NovAtel GSV 4004B can track up to 3 geostationary SBAS satellites in addition to GPS

Total Electron Content

Absolute TEC: TEC = TECR - ( b

R + b

S )

Relative TEC: TECR = TEC

+ <TECP – TEC>ARC

bR - Receiver/station bias (TECU)

bS - Satellite bias (TECU)

TECP - Differential pseudorange (TECU)

TEC - Differential carrier phase (TECU)

< >ARC

- Average over phase-connected arc

Estimation of absolute TEC using GPS involves two steps:

- Levelling the phases to the pseudorange gives the relative TEC

- Estimation/removal of instrumental biases (calibration) gives absolute TEC

TEC

TECP

UT (hours)

TE

CU

GPS-SCINDA (*.scn file) provides TECP and TEC

WinTEC-P uses these to estimate absolute TEC

Types of GPS Satellite Biases to Remove

The technique used by the receiver to measure the pseudoranges dictates how the satellite instrumental biases should be removed.

Receiver Model Method used to measure the DPR Type of Satellite Bias to Remove

Ashtech Z-12 L2(P2) - L1(P1) P1P2 bias

Ashtech µZ-CGRS L2(P2) - L1(P1) P1P2 bias

NovAtel GSV 4004B L2(P2) - L1(CA) P1P2 bias minus the P1C1 bias

Files containing monthly estimates for the P1P2 and P1C1 biases can be downloaded from the Center for Orbit Determination in Europe (CODE) at this URL: http://www.aiub.unibe.ch/download/CODE/.

These satellite differential codes bias are not absolute timing biases, instead they average to zero. The unknown offset is immaterial in that it will be lumped together and removed along with the receiver bias.

The WinTEC-P Software for TEC Calibration

Here we discuss only the use of the software. For the theoretical basis of this technique see:

Carrano, C. S., A. Anghel, R. A. Quinn, K. M. Groves (2009), Kalman Filter Estimation of Plasmaspheric TEC using GPS, Radio Sci., 44, RS0A10, doi:10.1029/2008RS004070.

and also our talk scheduled later in this workshop:

Carrano, C.S., A. Anghel, K. M. Groves, Separating the Ionospheric and Plasmaspheric Contributions to GPS Measurements of Total Electron Content.

Compiling the WinTEC-P Program

• The WinTEC-P software is distributed with gps-scinda-bundle and will be compiled automatically (as needed) on the GPS-SCINDA data collection computer.

• However, you can compile WinTEC-P on any computer running LINUX.

• To compile WinTEC-P from source, the GNU Scientific Library and GNU R are required (both are free). For Debian Linux, these can be installed by logging in as root and typing:

apt-get updateapt-get install libgsl0-dev r-base

• The WinTEC-P software can then be compiled from the source code as follows:

tar xzvf wintec-p-src-1.05.tar.gzcd wintec-p-src-1.05./configuremake

• This will create executables named “wintec-p” and “download_biases”.

Generating Plots of S4 and TEC Manually

• Make sure the files wintec-p.conf, s4.conf, and tec.conf are located in the current directory along with the wintec-p executable and the scripts s4.r and tec.r. One can process an arbitrarily long sequence of ionospheric statistics files (*.scn) with WinTEC-P as follows:

./wintec-p -d -r 090601_000000.scn 090601_010000.scn … 090601_230000.scn

• The coordinates of the station are obtained from corresponding *.psn files (if present), or

they must be specified in the wintec-p.conf configuration file. Plots of S4 and calibrated

TEC are generated using GNU R as follows:

R --slave < s4.rR --slave < tec.r

• Alternatively, you can run a script called “wintec-p-daily.pl” to automate this process:

./wintec-p-daily.pl *.scn

• This will group the hourly input files into daily batches, which will be processed by wintec-p and then R to create daily plots.

Command Line Options for WinTEC-P

• The wintec-p program creates a file called restart.dat when it finishes. This file contains the last Kalman state. When you are processing new data and wish the Kalman filter to restart from its last saved state, supply the “-r” command line option, e.g.:

./wintec-p –r 090602_000000.scn 090602_010000.scn … 090602_230000.scn

If the restart.dat file cannot be found, the Kalman state will be initialized to zero.

• Depending on the options selected in the configuration file wintec-p.conf, the wintec-p program can estimate the satellite biases from the data, or it can use satellite biases downloaded from CODE.

The “-d” command line option indicates that wintec-p should attempt to download the appropriate differential code bias files from CODE automatically using “wget”:

./wintec-p –d 090602_000000.scn 090602_010000.scn … 090602_230000.scn

This download requires Internet access. If Internet access is unavailable or unreliable, it’s probably best to have wintec-p estimate the satellite biases from the data.

Example of Plots Generated Using WinTEC-P

GPS Scintillation Intensity Total Electron Content

One can also generate separate plots for each satellite to see greater detail.

Output of the WinTEC-P Program

/home/gps/plots

/home/gps/processed_data

090524_tec.dat.gz – calibrated TEC090524_res.dat.gz – post-fit residual090524_cov.dat.gz – covariances090524_state.dat.gz – Kalman state090524_model.dat.gz – zenith TEC estimates (ionosphere & plasmasphere)090524_biases.dat.gz – Estimated receiver and satellite biases

YYMMDD – Time tag format (UTC)

S20090524.PNG - Scintillation intensity index (S4)

T20090524.PNG – calibrated TEC

When WinTEC-P is run automatically on the data collection computer, output files are created here:

If “no” is selected for the “archive calibrated TEC” option when configuring the software, these files will be overwritten each time (to save disk space on the data collection computer)

Format of the Calibrated TEC File (tec.dat)

#YYMM DD UTSEC AZ EL PLAT PLON PCGLAT PCMLT S4 DPR PTEC STEC STECE VTEC VTECE PRN09 06 02 82822 322.10 47.40 -35.76 45.37 -44.27 25.77 0.05 -0.27 0.00 1.65 80.38 1.26 61.65 0309 06 02 82822 347.50 44.60 -35.02 46.62 -43.72 25.88 0.04 -0.46 0.00 2.89 80.41 2.13 59.33 0609 06 02 82822 215.00 15.90 -44.57 40.67 -50.54 25.10 0.10 12.73 0.00 -1.00 -1.00 -1.00 -1.00 1109 06 02 82822 154.40 13.10 -46.32 53.32 -53.27 25.79 0.26 9.19 0.00 -1.00 -1.00 -1.00 -1.00 1409 06 02 82822 10.90 18.70 -30.60 49.03 -40.06 26.19 0.17 2.10 0.00 -1.00 -1.00 -1.00 -1.00 1609 06 02 82822 276.50 52.60 -37.61 44.58 -45.69 25.65 0.05 5.05 0.00 3.52 80.38 2.88 65.72 1909 06 02 82822 298.00 25.50 -35.07 41.28 -43.59 25.54 0.10 16.46 0.00 7.70 80.42 3.99 41.63 2309 06 02 82822 91.50 53.50 -37.92 50.16 -46.28 25.98 0.05 1.85 0.00 2.98 80.35 2.46 66.36 31

YY – 2 digit yearMM – monthDD – dayUTSEC – seconds since midnightAZ – azimuth (deg)EL – elevation (degPLAT – latitude of IPP (deg)PLON – longitude of IPP (deg)PCGLAT – magnetic latitude of IPP (deg)PCMLT – magnetic local time of IPP (hrs)

S4 – Scintillation intensity indexDPR – Differential pseudorange (TECU)PTEC – plasmaspheric slant TEC (TECU)STEC – ionospheric slant TEC (TECU)STECE – estimated error in STEC (TECU)VTEC – vertical equivalent TEC (TECU)VTECE – estimated error in VTEC (TECU)PRN – pseudorandom noise satellite identifier

-1 indicates missing values (e.g. elevation too low)

Legend:

Format of the Biases File

WINTEC GNSS C1-P2 DCB SOLUTION, ENDING D153, 2009 03-JUN-09 23:55--------------------------------------------------------------------------------

DIFFERENTIAL (C1-P2) CODE BIASES FOR SATELLITES AND RECEIVERS:

PRN / STATION NAME VALUE (TECU) RMS (TECU)*** **************** *****.*** *****.***G01 0.000 316.228G02 -15.712 56.796G03 7.520 56.796G04 7.478 56.796G05 0.000 316.228G06 7.711 56.796G07 1.397 56.796G08 9.441 56.796G09 4.433 56.796G10 7.671 56.796

... ... ...

G30 5.820 56.796G31 -5.805 56.796G32 8.778 56.796REC 31.053 56.796

The WinTEC-P Configuration File

# Estimate the plasmaspheric TECestimate_plasmasphere = 0

# Estimate the receiver biasestimate_rx_bias = 1

# Estimate the satellite biasesestimate_sat_biases = 1

# Force TEC to be non-negativenon_negative_tec = 1

# Set to 1 for receivers that track C/A code on L1, 0 for receivers that track P code on L1p1c1 = 1

# Use the last bias estimates from the Kalman filter (to avoid transients)use_last_biases = 1

# Use the last plasmaspheric scaling factor from the Kalman filter (to avoid transients)use_last_plasmasphere = 1

# Specify the path to the satellite biases from CODEpath_to_biases = ./biases

The configuration file wintec-p.conf specifies the options to use when calibrating the TEC:


# Assumed altitude of the ionospheric penetration point in km# alt_ipp = 350.

# The elevation mask# elmask = 20.0

# Geographic latitude of the station in degrees (only used if no *.psn file is available)# slat = 0.0

# Geographic longitude of the station in degrees (only used if no *.psn file is available)# slon = 0.0

# Geographic altitude of the station in degrees (only used if no *.psn file is available)# salt = 0.0

# Max attained by Kp index over the past 24 hours (only used if estimate_plasmasphere > 0)# kpmax = 1.0

# 13 month average sunspot number (only used if estimate_plasmasphere > 0)# rbar = 7.9


# Automatically download the satellite biases from CODE# download = 0

# Restart the Kalman filter from a previously saved state# restart = 0

# Print debugging information# debug = 1

The S4 Configuration File

# Name of station (can be left blank)site =

# Range for the time axis (set equal to -1 to autoscale)hr_min = 0hr_max = 24

# Maximum value of S4 to plots4_max = 1.2

# Type of output (bitmap,png,ps,eps)output_type = bitmap

The configuration file s4.conf specifies the options for plotting the S4 index using the

GNU R script s4.r:

The TEC Configuration File

# Name of station (can be left blank) site =

# Variable to plot (vtec,stec,ptec) tec_type = vtec

# Plot versus (ut=ut, mlt=mlt of IPP) time_type = mlt

# Units for the time axis (min,hr) time_units = "hr"

# TEC Range (set tec_max=0 to autoscale) tec_min = -2 tec_max = 60

# Type of output (bitmap,png,ps,eps) output_type = bitmap

# Plot type (no=all data on one page, yes=separate pages for each PRN) multipage = no

The configuration file tec.conf specifies the options for plotting the TEC using the GNU R script tec.r:

Questions?

Appendix

Multipath

Mounting the GPS Antenna

GPS Antenna should be installed high, with minimal obstructions from buildings, other antennas and equipment, power lines, and trees. Antenna cable length should not exceed 30 m to limit signal losses.

GPS antenna

Important: Moving the antenna or changing cables can change the receiver bias.

GPS Multipath

Only the portion of the signal that travels along the direct path from the satellite is useful. All other contributions are called multipath.

Signal interference at the antenna due to multipath causes fluctuations that can resemble scintillation, but these fluctuations are not caused by the ionosphere.

Multipath and Scintillation

Day 53

Day 54

Day 55

Day 56

Day 57

Day 58

Day 59

The pattern of multipath scintillation changes slowly from day to day (due to the 4 minute daily rotation of the GPS constellation)

Ionospheric scintillation changes quasi-randomly from day to day and is superimposed on the multipath background

Multipath due to ground-based obstructions of the sky is usually encountered at low elevations

Data from Ascension Island in 2006

System Maintenance

Logging into the Linux Console

1. Press the Ctrl + Alt + F2 keys at the same time to change to the Linux console

2. You should now see a login prompt that looks like this (the hostname “cvd-gps” may be different for your computer):

cvd-gps login:

3. At the prompt type root and press enter

4. You should now see a prompt that looks like this:

password:

5. At the prompt type the password: gpspassw

NOTE: all characters are case-sensitive (also, the root password for your computer may be different).

6. You should now see a prompt that looks like this:

cvd-gps:~#

7. At the prompt type whatever commands are necessary for maintenance.

8. To log out again, type logout at the prompt and press enter

9. Press the Ctrl + Alt + F1 keys at the same time to return to the GPS display

Rebooting the Computer


2. Log in to the Linux console as described on the previous slide. You should now see a prompt that looks like this

(the hostname “cvd-gps” may be different for your computer):

cvd-gps:~#

3. Type /sbin/reboot

4. The computer will shut down and then restart.

If you want to shut down the system instead of rebooting it, type /sbin/halt instead of /sbin/reboot in step 3.

Performing Monthly CDROM Backups


2. Log in to the Linux console as the root user (as described on an earlier slide). You should now see a prompt that looks like this (the hostname “cvd-gps” may be different for your computer):

cvd-gps:~#

3. At the prompt type

cd /home/gps

and press the enter key. The prompt should then read:

cvd-gps :/home/gps#


./monthly-backup.pl 09/2005

where "09" is month and "2005" is the year to be backed up, Sep 2005 in this example. For October 2005 you would enter

“./monthly-backup.pl 10/2005” and so on. Note that there is a “period” before the forward slash at the beginning.

5. The screen will scroll quickly, listing the files to be backed up. This is normal.

The computer will ask if you wish to burn a CD now. Verify that there is a blank CD in the drive, type y for yes, and press enter.

The CD will now record; if it requires more than one CD to complete, the written CD will eject and it will prompt you to insert a new CD. Do this as prompted, close the drive, and type y again to continue.

6. Upon completion, label the CD's with 3 items: Location, month/year being backed up, and date the back-up was made

7. At the prompt type logout and press enter.


Editing a File at the Linux Console


2. Log in to the Linux console as described on the previous slide. You should now see a prompt that looks like this (the hostname “cvd-gps” may be different for your computer):

cvd-gps:~#

3. Any command line text editor, such as vi or nano, may be used to edit files under Linux. A particularly simple editor is nano, since it shows the commands used to do basic editing tasks at the bottom of the screen while you edit the file. The nano user interface is shown below:

To move the cursor use the arrow keys on the keyboard

To save the file you are editing, type Ctrl+O

To exit the editor, type Ctrl+X

4. After you are done editing and have exited nano, type logout at the prompt and press enter.


Configuring the Network Settings


2. Log in to the Linux console as described on an earlier slide. You should now see a prompt that looks like this (the hostname “cvd-gps” may be different for your computer):

cvd-gps:~#


cd /etc/network/

and press the enter key. The prompt should then read:

cvd-gps: /etc/network/ #

4. Bring up the file “interfaces” in nano for editing by typing nano interfaces at the prompt and hitting enter. The screen should look like this:

5. Move the cursor with the arrow keys on the keyboard and update the address, netmask, and gateway according to the directions of your local network administrator. After you have made the changes, press Ctrl+O to save them, and Ctrl-X to exit the editor.

6. Reboot the computer by typing /sbin/reboot at the prompt and then pressing enter.

7. The new network settings should take effect after the computer reboots.

File Formats

GPS-SCINDA Data Logging

• GPS L1 signal (1575 MHz)

– S4 scintillation index

• GPS L2 signal (1228 MHz)

– S4 scintillation index (not useful with semi-codeless tracking)

• Both the L1 and L2 signals

– Total Electron Content (TEC)

– Rate of TEC Change (ROTI)

• Raw amplitude and phase data (50 Hz) can be recorded as desired

What we measure: GPS-SCINDA System Outputs

GPS Data File Formats

GPS-SCINDA writes several different types of data files, each with its own unique (free) format.

New data files are created hourly and are named according to the date and time using the format YYMMDD_hhmmss.* below:

Filename Format

YY Two digit year

MM Month (01-12)

DD Day of month (01-31)

hh Hour (00-23)

mm Minute (00-59)

ss Second (00-59)

For example, the filename for data collected starting 1 July 2006 at 12:00 UT would be 060701_120000.scn.

The types of files that may be generated by the GPS system include the following:

Filename Extension File Contents

*.scn Ionospheric statistics

*.psn Receiver position

*.msg Error log and diagnostic messages

*.nvd Raw data

Ionospheric Statistics File (*.scn) Format

Time-tag Format

T The character “T” in the leftmost column

YY Two digit year

MM Month (01-12)


SSSSS Seconds since midnight (00000-86399)

Column Ionospheric Statistics Data (*.scn)

1 Azimuth (deg)

2 Elevation (deg)

3 Scintillation index (S4) of the carrier code on L1

4 Percent samples taken at L1, compared to number expected (0-100%)

5 Scintillation index (S4) of the P - code on L2

6 Percent samples taken at L1, compared to number expected (0-100%)

7 Differential pseudo-range in TEC units

8 Differential carrier phase in TEC units (with unknown additive offset)Standard deviation of rate of change of TEC over one minute9

10 TEC in TEC units

11 Number of minutes since running average of TEC has been restarted

12 PRN number

The scintillation data (*.scn) records are provided each minute. Each satellite tracked is assigned its own row, whose columns are:

Each data record in the *.scn files is preceded by a time-tag of the form: "T YY MM DD SSSSS", followed by the actual data in the record. The format of the time-tag is described in the table below:

A Sample Ionospheric Statistics File (*.scn)

Below is an example showing two records of data from an ionospheric statistics (*.scn) file, each containing parameters for three tracked satellites.

Sample *.scn file

T 03 09 30 42972132.3 55.0 0.12 100 0.06 100 52.4 -1.105 0.78 38.1 74 09 52.0 38.0 0.16 100 0.09 100 23.8 13.767 1.37 35.9 76 26 57.0 20.0 0.10 100 0.03 100 52.8 5.995 0.80 60.3 16 29T 03 09 30 43032131.8 55.6 0.07 100 0.03 100 50.1 -1.106 0.65 38.3 75 09 52.0 37.5 0.13 100 0.09 100 30.6 14.071 1.18 36.1 77 26 57.0 19.3 0.10 100 0.07 100 55.6 6.526 0.81 60.5 17 29

...

...

Position File (*.psn) Format

Time-tag Format

T The character “T” in the leftmost column

YY Two digit year

MM Month (01-12)


SSSSS Seconds since midnight (00000-86399)

The position records are provided every second. A time-tag is assigned only once per minute, but following it will be 60 receiver position updates at one second intervals. The columns of the position records are of variable length, depending on how many satellites are tracked:

Each data record in the position files (*.psn) is preceded by a time-tag of the form: "T YY MM DD SSSSS", followed by the actual data in the record. The format of the time-tag is described in the table below:

Column Position Data (*.psn)

1 Latitude (deg)

2 Longitude (deg)

3 Altitude (m)

4 Number of satellites tracked

5-17 PRN followed by ”U” if it is used in position solution, “-” otherwise.

A Sample Position File (*.psn)

Below is an excerpt from a position file (*.psn), showing the receiver position and tracking information for the two minutes beginning at 40752 and 40812 seconds since midnight.

Sample *.psn file:

T 03 09 30 4075242.4819653 -71.2634513 68.379 04 26U 10U 17U 09U42.4819652 -71.2634527 68.344 04 26U 10U 17U 09U42.4819650 -71.2634525 68.421 04 26U 10U 17U 09- ... ... 57 more samples follow ...

T 03 09 30 4081242.4819648 -71.2634532 68.421 04 26U 10U 17U 09-42.4819650 -71.2634547 68.355 04 26U 10U 17U 09-42.4819653 -71.2634513 68.379 04 26U 10U 17U 09U ... ... 57 more samples follow ...

Statistics Ashtech Z-12 Ashtech Z-CGRS NovAtel GSV 4004B

Az, El 1 Hz 1 Hz 1 Hz

Lat, Lon, Alt 1 Hz 1 Hz 1 Hz

SV's tracked/used 1 Hz 1 Hz 1 Hz

S4 measured using L1(CA) 20 Hz 10 Hz 50 Hz

S4 measured using L2(P2) 2 Hz 10 Hz 1 Hz

TECP 2 Hz 10 Hz 1 Hz

TEC 20 Hz 10 Hz 1 Hz

ROTI 20 Hz 10 Hz 1 Hz

TEC 20 Hz 10 Hz 1 Hz

Raw Data Rates for Different GPS Receiver Models

remote sensing the ionosphere using gps-scinda dr. charles carrano 1 dr. keith groves 2 1 institute...

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