Transcript Laramie Potts, Engineering Technology - NJIT Advance

High Resolution GPS-TEC Gradients in the Northern Hemisphere
Ionospheric Trough
Continuous Operational Reference Station (CORS) network in
New Jersey (see map) is a network of GPS stations that
provide continuous dual frequency (fL1, fL2) measurements.
Modeling the altitude dependency of electron density by a
Chapman profile yield estimate of TEC. A recent GPS
acquisition at Jenny Jump (NJJJ), NJIT’s experimental station
equipped with magnetometer and other imaging instruments,
should add new insights on ionospheric trough dynamics and
related variables of space weather research.
Laramie V. Potts
New Jersey Institute of Technology
Department of Engineering Technology
Newark, NJ 07102-1982 ([email protected])
Abstract:
Latitudinal Profile of Ionospheric TEC from Altimetry
The intent of this work is to integrate GPS observations at
NJJJ with the NJ CORS GPS network to produce high spatial
and temporal TEC maps. These GPS-derived TEC maps, in
turn, will provide new high resolution data to search for short
wavelength gradients in the mid-latitude ionospheric trough.
Ionospheric modeling using dual frequency geospatial mapping (Satellite Altimetry) and
satellite-based positioning (GPS) data is the focus of extensive research in space
weather systems [1]. The poorly understood complex dynamics of ionospheric
irregularities and external field variability over the mid-latitude regions are not well
explored due to limitations of empirical models. The limited accuracy in predicting
ionospheric effects presents significant problems affecting communication, remote
sensing, surveillance, navigation and climate change research. However, currently
available space geodetic sensors can facilitate substantial improvements on modeling
ionospheric Total Electron Content (TEC) from various ground- and space-based
observations [2]. These observations include the GPS derived Global Ionosphere Maps
(GIMs) generated by the mapping of the slant radar signals (L-band) from satellite
(20,000 km) to the global ground receiver station network at each receivers’ zenith
direction [3], LEO’s (400 km -1300 km, in the F and H ionosphere regions) carrying GPS
receivers, and EnviSat (750 km) dual-frequency altimeter observations. Comparison with
high spatial and temporal resolution GPSTEC from CONUS and CORS network is
expected to provide new insight on short wavelength variability in the mid-latitude
ionospheric trough. The Figure below is an example of the low resolution GPSTEC over
most of North America
Major factors that determine TEC are intensity of solar activity,
season, position, altitude, etc. Previous studies suggest that
strong latitudinal gradients are associated with the ionospheric
trough. However, the physical mechanisms of the trough
formation include complex interconnected physical processes
that are not well studied. Integrating NJJJ with the NJ CORS
network may further our knowledge on small scale structure
and related dynamic processes.
Data and Models
Nadir ionosphere delay over oceans and large lakes is measured by dual- frequency
altimeters. Dual frequency altimeters such as Envisat, carrying a Ku-band (13.575 GHz)
ad S-band (3.2 GHz) altimeter at 800 km, measures the fluctuations in TEC between the
satellite and the earth’s surface to remove ionospheric influence and obtain a better
estimate of altitude. Measured height at a given frequency hf is given by :
A  TEC
with A = 40250.
hf  h 
f2
TEC obtained from altitudes (ranges) from two frequencies hKu and hs as:
The transient location of the ionospheric trough is
dependent on season, time, and geomagnetic
activity
as
represented
by
Kp
index.
Experimental GPS TEC data was used to
develop the trough location. The model is
represented by a Fourier expansion of degree 2
as;
4
4
 ( LT )  b2 sin(  LT )  a2 cos(  LT )
24
24
2
2
 b1 sin(
 LT )  a1 cos(
 LT )  a0
24
24
(hs  hKu ) f Ku2 f s2
TECAlt (m m) 
,
2
2
A( f Ku  f s )
with coefficients a0 , a1 , a2 , b1 , b2 to be determined
GPSTEC is calculated using a mapping function (Figure below)
to estimate vertical TEC (VTEC) using group path lengths from
two frequencies (L1=1.575GHz and L2=1.2276 GHz)
Background
Trough Location
Geomagnetic storm indicators are indices such as Kp, Dst, and
AE. Values for the Dst parameter ranges from low positive
values for quiet times to high negative values to indicate storm
activity. Figures below show solar activity for January and
February of 2009 as derived from the Dst parameter. No
storms were reported for 2009.

60º
Ionospheric
Piercing Point
50º
The structure and dynamics of the ionospheric trough over North America, monitored from
GPS observations, suggest that enhanced variability is mainly due to geomagnetic storm
activity [2]. Maximal latitudinal gradients occur at the equatorial and polar walls of the 5º7º trough. Over the mid-latitude regions of North America, the spatial distribution of TEC
variability may be associated with perturbations in the neutral winds and other geophysical
conditions. Geomagnetic storm indicators are indices such as Kp, Dst, and AE – the Kp,
parameter is used to devise an empirical model [4] of the transient location of the midlatitude ionospheric trough, while the Dst parameter is sensitive to storm activity.
'
40º
30º
12hr

18hr
0hr
6hr
Local Time
12hr
Ionosphere
Why Study Ionosphere TEC in the Mid-latitude Trough?
TEC is a key ionospheric parameter for
• space-ground telecommunication system,
• satellite navigation systems,
• satellite orbit determination,
• ocean altimetry for tide modeling and sea level rise,
• remote sensing, and
• ionospheric seismology
CONUS and CORS stations provide measurement network in the mid-latitude region to
study ionospheric variability with high spatial and temporal resolution for clues on the
complex interconnected physical processes of the trough formation.
VTECGPS  TECslant cos  '
References
hm
Earth
Surface
where
RE
sin  ' 
sin 
RE  hm
Sub-ionospheric
Point
1) Brunini,C., A. Meza, W. Bosch, Temporal and spatial variability of the bias between TOPEX- and GPSderived total electron content, J. Geodesy, 79, 175-188, 2005.
2) Araujo-Pradere, E. A., T. J. Fuller-Rowell, P. S. J. Spencer, and C. F. Minter, Differential validation of the
US-TEC model, Radio Science, V42, RS3016, doi:10.1029/2006RS003459, 2007.
3) Ya’acob, N., M. Abdullah, M. Ismail, Determination of GPS Total Electron Content using Single Layer
Model (SLM) Ionospheric Mapping Function, Inter. J. Comp. Sci. Network Security, 8(9), 154-160, 2008.
4) Krankowski, A., I. Shagimuratov, I. Ephishov, A. Krypiak-Gregorczyk, The occurrence of the mid-latitude
trough in GPS-TEC measurements, Advances in Space Research, [in press], 2009.