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  • GIRO provides accurate specification of electron density in the Earth's ionosphere at >60 locations in the world
  • 37 GIRO locations provide real-time ionospheric data to the central server in Lowell, Massachusetts within several minutes
  • GIRO sites are equipped by Digisonde instruments that use high frequency remote sounding technique to probe bottomside ionosphere from 80 km up to the peak of ionospheric plasma density
  • Real-time and retrospective data from GIRO locations are ingested in Lowell Digital Ionogram DataBase (DIDBase)
  • GIRO data are opened for public access via DIDBase and DriftBase Web Portals, and custom software tools for digisonde data analysis, SAO Explorer and Drift Explorer
  • Please make sure to read Rules of the Road

Contact: Prof. Bodo W. Reinisch, LDI
Prof. Ivan A. Galkin, UMLCAR

Digisonde Evolution

Digisonde 4D
  • Digisonde is an ionospheric radar, ionosonde, that uses high frequency (HF) radio waves for the vertical-incidence remote sounding of the ionosphere, a technology incepted by Sir Edward Appleton in the late 1920s
  • Digisonde is an acronym for Digital Ionospheric Goniometric Ionosonde
  • Digisonde belongs to a class of advanced ionosondes that evaluate angle of arrival, polarization, and Doppler frequency shift of skywave signals reflected from the ionosphere, in addition to their travel time that is conventionally used to determine range to the reflection point
  • The first Digisonde was deployed at Eglin AFB in Florida in 1969
  • 123 digisondes have been built by UMLCAR engineers as of March 2010
  • Full station list by instrument is here
  • Digisonde ionogram presents signals reflected from the ionosphere in the frequency vs travel time frame, with signal strength indicated by the pixel intensity, and wave polarization, angle of arrival, and Doppler frequency indicated by colors
  • Individual reflected signals (echoes) observed on each sounding frequency form traces in the ionogram image
  • Red (green) colors indicate vertical echoes with O-polarization (X-polarization)
  • ARTIST software scales the ionogram and calculates the vertical Electron Density Profile (EDP) in real time
  • Thin black lines show the ARTIST-identified O-traces
  • The black line with uncertainty bars shows the calculated bottomside EDP
  • Extraction and interpretation of the signal traces in ionogram images is an intelligent, machine-hard problem of feature recognition
Digisonde Directogram
  • Digisonde Spread-F Directogram displays time history of echoes propagating off-vertically after reflecting from irregular plasma structures
  • Y-axis is time, and X-axis is horizonal distance in the ionosphere to the reflection point, with 0 corresponding to the sounder location
  • Vertical echoes are not shown; blank directogram means quiet (horizontally stratified) ionosphere
  • Signatures in the directograms indicate development of Spread F conditions
  • Doppler sign of echoes is analysed to label plasma structures approaching on one side and departing to the other side with the same color
  • In the example directogram, development and eastward drift of 8 plasma bubbles is detected by Cachimbo digisonde in Brazil
SAO Explorer
  • SAO Explorer is the flagship software tool for working with GIRO ionograms
  • SAO-X has capability of accessing ionograms and ionogram-derived data from 60+ locations in the Lowell DIDBase (via TCP/IP port 3050)
  • DIDBase is Digital Ionogram DataBase
  • 14+ million ionogram images
  • 15+ million ionogram-derived records
  • Web Portal access for image browsing

Common SAO Explorer Data Visualizations and Tools

Ionogram Editor
  • Interactive ionogram scaling environment
  • Mouse-driven leading edge highlighter
  • ARTIST-5 autoscaling algorithm to reduce overall manual effort
  • Profile inversion algorithm NHPC
  • Visualization controls, including content selectors, data labels, and detail-on-demand context window

Time Series
  • Time series of common ionospheric characteristics
  • IRI-2001 model values available for comparisons
  • Plain text export for external data analysis

  • Time history of the vertical profile of electron density
  • X axis is time, Y axis is altitude, and color is mapped to plasma density
  • Example from Millstone HIll observatory illustrates ionospheric response to a strong interplanetary shock event


Doppler Skymap:

  • Skymap presents ionospheric echoes in 2D sky coordinate system that maps the echoes ("sources") onto a 2D fundamental skymap plane using their azimuth and zenith arrival angles, thus discarding the range information
  • The skymap plane presents the zenith angle as radius and azimuth angle as polar angle of the polar coordinate system
  • Color is mapped to the Doppler frequency shift, with red shades corresponding to receding plasma, blue shades - to approaching plasma, and green shades - to slowly moving plasma
  • Observed Doppler frequency shift is converted to the light-of-sight (LOS) velocity that is further split into horizontal and vertical components
  • Drift Data Analysis (DDA) technique treats the whole area of ionosphere illuminated by Digisonde signal as a single entity moving at the same bulk drift velocity
  • DDA uses the least squares fit method to obtain best fit of all sources visible on the skymap with their individual Dopper velocities to compute the LOS bulk velocity vector
  • Calculated horizontal and vertical drift velocity components are shown in the skymap using the arrow symbols
  • Skymaps are also used to determine the center of reflections that corresponds to the large-scale tilt of the ionospheric plasma distribution in the reflecting area
  • The example from Trivandrum digisonde in India shows a classic nighttime zonal drift of ionization bubbles across the station from West to East

Time series of the DDA bulk drift velocity:

  • Drift velocity vector is presented by one chart of the vertical velocity component Vz and two charts of the horizontal velocity components that can use either Cartesian (East and North components ) or cylindrical (asimuth and radial components) representations
  • Error bar indicate how well the bulk velocity vector represents underlying skymap sources
  • Larger error bars correspond to greater deviation of observed plasma motions in the skymap from the collective bulk motion assumed by DDA algorithm
  • Local sunrise and sunset times are labeled appropriately in the central panel of the plot
  • This example velocity plot from Trivandrum digisonde shows classic signatures of the equatorial plasma drift: (1) westward daytime zonal drift at ~270° azimuth, (2) eastward mighttime drift at ~90° azimuth, and (3) vertical uplift of the plasma in response to the pre-reversal enhancement of the electric field during evening hours
Drift Velocities
Drift Explorer
  • Drift Explorer is the main software tool for working with GIRO ionospheric drift data using DDA technique
  • Drift-X has capability of accessing drift data records, including raw receive channel data and derived data (skymaps, ionospheric tilt, velocity time series) from 39 locations in the Lowell DriftBase (via TCP/IP port 3050)
  • 7+ million raw drift data measurements
  • 5+ million Doppler skymaps
  • 5+ million drift velocity records
  • Web Portal access for image browsing

Common Drift Explorer Data Visualizations and Tools

Skymap Plotting Screen
Skymap Plotting Screen
Interactive skymap browser
Skymap Survey
Ionogram Editor
  • Separate panels for drift in E and F regions of the ionosphere
  • Detail-on-demand window for extended data display at the crosshair pointer position
  • Display of frequency and height intervals where the raw drift data were acquired for velocity calculations