Data Access
These ionograms were digitized from the original ISIS-2 7-track analog telemetry tapes using the facilities of the former Data Evaluation Laboratory at the NASA/GSFC. This data restoration project is headed by Dr. R.F. Benson (NASA/GSFC). Ionograms were digitized at the rate of 40,000 16-bit samples/sec. This sample rate is higher than the Nyquist frequency of 30 kHz. The sample frequency of 40 kHz provides a measurement every 25 microseconds corresponding to an apparent range (c*t/2) interval of 3.75 km. Ionograms with this sample rate are designated as "full" ionograms because they have the full 3.75 km apparent-range resolution. The ionograms used for most analysis, and those available from CDAWeb, were produced by averaging every four samples of the sounder-receiver video amplitude output to yield an average value every 100 microseconds corresponding to an apparent-range resolution of 15 km. These ionogram files are referred to as "average" files with standard resolution. Each ionogram consists of a fixed-frequency and and a swept-frequency portion. The time resolution between ionograms is typically 14 or 22 seconds depending on the frequency sweep range.
Version:2.2.9
These ionograms were digitized from the original ISIS-2 7-track analog telemetry tapes using the facilities of the former Data Evaluation Laboratory at the NASA/GSFC. This data restoration project is headed by Dr. R.F. Benson (NASA/GSFC). Ionograms were digitized at the rate of 40,000 16-bit samples/sec. This sample rate is higher than the Nyquist frequency of 30 kHz. The sample frequency of 40 kHz provides a measurement every 25 microseconds corresponding to an apparent range (c*t/2) interval of 3.75 km. Ionograms with this sample rate are designated as "full" ionograms because they have the full 3.75 km apparent-range resolution. The ionograms used for most analysis, and those available from CDAWeb, were produced by averaging every four samples of the sounder-receiver video amplitude output to yield an average value every 100 microseconds corresponding to an apparent-range resolution of 15 km. These ionogram files are referred to as "average" files with standard resolution. Each ionogram consists of a fixed-frequency and and a swept-frequency portion. The time resolution between ionograms is typically 14 or 22 seconds depending on the frequency sweep range.
| Role | Person | StartDate | StopDate | Note | |
|---|---|---|---|---|---|
| 1. | PrincipalInvestigator | spase://SMWG/Person/James.H.Whitteker | |||
| 2. | GeneralContact | spase://SMWG/Person/Robert.F.Benson | |||
| 3. | GeneralContact | spase://SMWG/Person/Dieter.K.Bilitza |
ISIS/Alouette page maintained by NASA GSFC with science and instrument descriptions, data access, software, and publication lists
Information about the Sweep Frequency Sounder experiment on ISIS-2.
FTP access to repository of ISIS-2 Ionograms in CDF format at NASA CDAWeb. The CDF files are organized by ground station, where each ground station is represented by a three letter ID and a two-digit code. The full names for each station are provided at https://nssdc.gsfc.nasa.gov/space/isis/isis-table1-new.html A merged data set, independent of the ground stations, is planned.
HTTPS access to repository of ISIS-2 Ionograms in CDF format at NASA CDAWeb
CDAWeb interactive interface for subsets, plots and lists of data
ISIS-2 Topside Sounder Average Ionogram over Ahmedabad, India: AME, Latitude 23, Longitude 73
ISIS-2 Topside Sounder Average Ionogram over Ascension Island, United Kingdom: ACN, Latitude -8, Longitude 346
ISIS-2 Topside Sounder Average Ionogram over Brazzavillle, Congo: BRZ, Latitude -4, Longitude 15
ISIS-2 Topside Sounder Average Ionogram over Fairbanks, AK: ULA, Latitude 65, Longitude 212
ISIS-2 Topside Sounder Average Ionogram over Falkland Island, United Kingdom: SOL, Latitude -52, Longitude 302
ISIS-2 Topside Sounder Average Ionogram over Johannesburg, South Africa: BUR, Latitude -26, Longitude 28
ISIS-2 Topside Sounder Average Ionogram over Kashima, Japan: KSH, Latitude 36, Longitude 141
ISIS-2 Topside Sounder Average Ionogram over Kerguelen Island, France: KER, Latitude -49, Longitude 70
ISIS-2 Topside Sounder Average Ionogram over Kourou, French Guyana: KRU, Latitude 5, Longitude 307
ISIS-2 Topside Sounder Average Ionogram over Kwajalein, Marshall Islands: KWA, Latitude 9, Longitude 168
ISIS-2 Topside Sounder Average Ionogram over Las Palmas, Canary Island, Spain: CNA, Latitude 28, Longitude 345
ISIS-2 Topside Sounder Average Ionogram over Lauder, New Zealand: LAU, Latitude -45, Longitude 170
ISIS-2 Topside Sounder Average Ionogram over Orroral, Australia: ORR, Latitude -36, Longitude 149
ISIS-2 Topside Sounder Average Ionogram over Ottawa, QC, Canada: OTT, Latitude 45, Longitude 284
ISIS-1 Topside Sounder Average Ionogram over Ouagadougou, Burkina Faso: ODG, Latitude 14, Longitude 359
ISIS-2 Topside Sounder Average Ionogram over Quito, Equador: QUI, Latitude -1, Longitude 281
ISIS-2 Topside Sounder Average Ionogram over Resolute Bay, NU, Canada: RES, Latitude 75, Longitude 265
ISIS-2 Topside Sounder Average Ionogram over Santiago, Chile: SNT, Latitude -33, Longitude 298
ISIS-2 Topside Sounder Average Ionogram over Syowa Base, Antartica: SYO, Latitude -69, Longitude 40
ISIS-2 Topside Sounder Average Ionogram over Sodankyla, Finland: SOD, Latitude 67, Longitude 27
ISIS-2 Topside Sounder Average Ionogram over Terre Adelie, Antarctica: ADL, Latitude -67, Longitude 140
ISIS-2 Topside Sounder Average Ionogram over Tromso, Norway: TRO, Latitude 70, Longitude 19
ISIS-2 Topside Sounder Average Ionogram over Winkfield, United Kingdom: WNK, Latitude 51, Longitude 359
sat.-ID: 1=AL1, 2=AL2, 3=ISIS1, 4=ISIS2
two-digit telemetry station code
trans. power code: 1=Prim(400W) 2=Sec(400W)
sounder/receiver code: 0=off, 1=on
swept-f range code: 0=normal (swept-frequency from 0.1 to 10.0 MHz), 1=extended (swept-frequency from 0.1 to 20.0 MHz)
DMODE (transm. on/off for alternate frame pairs): 0=off, 1=on
GMODE (transmission of alternate frames of fixed-frequency ionograms and normal combined fixed- and swept-frequency ionograms): 0=off, 1=on
sounder mixed mode (transmission at a fixed-frequency while the sounder receiver sweeps over swept-frequency range): 0=off, 1=on
AIT mode (automatic sounder operation every 3 min): 0=off, 1=on
fixed frequency code: 0=off, 1=0.12, 2=0.48, 3=1.00, 4=1.95, 5=4.00, 6=9.303 MHz
Year of ionogram frame sync in UT
Day of Year of ionogram frame sync in UT
Hour of ionogram frame sync in UT
Minute of hour of ionogram frame sync in UT
Second of minute of ionogram frame sync in UT
Local Mean Time (hh,mm) at time of ionogram frame sync
geographic coordinates (Lat,Long,Hgt) at time of ionogram frame sync
Geomagnetic Local Time (HHMM) at time of ionogram frame sync
geomagnetic latitude at time of ionogram frame sync
geomagnetic longitude at time of ionogram frame sync
invariant latitude at time of ionogram frame sync
Dip angle of mag field direction at time of ionogram frame sync
Solar Zenith Angle at time of ionogram frame sync
L shell (McIlwain parameter) at time of ionogram frame sync
spacecraft in(=1)/out(=2) sunlight at time of ionogram frame sync
CEP instrument on(1)/off(0) status
VLF receiver on(1)/off(0) status
RPA instrument on(1)/off(0) status
IMS instrument on(1)/off(0) status
SPS instrument on(1)/off(0) status
EPD instrument on(1)/off(0) status
RLP instrument on(1)/off(0) status
ASP instrument on(1)/off(0) status
scan line number of start of swept-frequency portion of the ionogram - separates the fixed- and swept-frequency portions
msec after frame sync - time of frequency markers
ionogram frequency markers
each sounder-pulse transmission is followed by a scan of the sounder-receiver video amplitude output values for each delay time monitored after the transmitted pulse; these scans are called scan lines. There are two types of ISIS-2 binary ionogram files, one designated as "full" and one as "average" The full file has 892 delay times (one every 0.025ms). The average files are derived from the full files by averaging the amplitude values in 4 delay-time bins. Thus the average binary files contain 223 time-delay bins within each scan line. The cdf files were made from these average binary files.
Ionogram files can be of different length. In some the swept-frequency portion covers the range 0.1 - 10 MHz, in others 0.1 - 20 MHz. Also, the proper start of each ionogram file, marked by a frame-sync pulse, was not always detected during the analog-to-digital (A/D) conversion. In such cases a frame sync was inserted to limit the file size. Thus the number of sounder-receiver video amplitude vs. delay time scan lines per ionogram can vary.
delay-time values used in each scan line
apparent-range values used in each scan line
Time
The color scale represents a linear sounder-receiver video amplitude output range from zero to 4.5 V expressed in terms of telemetry units from zero to 255. This calibration is based on the video calibration levels at the end of the listening period following each sounder pulse (these calibration levels produce the multi-colored stripe at the bottom of the digital ionograms). The sounder-receiver automatic-gain-control (AGC) voltage (from 0 to 5.12 volts) is obtained from a linear interpolation between the AGC trace displayed between 2400 km virtual range (16.0 ms) as 5.12 V and either 2805 km (18.7 ms) on the average ionograms or 2801.25 km (18.675 ms) on the full ionograms2805 km (18.7 ms) as 0 volts. On the average ionograms, which are available as either CDF or binary files from the NSSDC, the range resolution is 0.1 ms (corresponding to a virtual-range resolution of 15 km) there are 28 rows (27 intervals) covering the 0 to 5.12 V range; thus each row in virtual range above (decreasing delay time) the zero level (at 18.7 ms delay time) corresponds to an increase of 5.12/27 V of AGC with a quantization uncertainty of approximately plus or minus 0.1 V. Two rows have zero video-output amplitude values (on the average ionograms) in order that a clear AGC trace is visible on the ionograms. The row with the greatest virtual range corresponds to the actual AGC value. These AGC values were obtained from the pcm data corresponding to the ionogram of interest; these pcm files are available from the NSSDC. If the ionogram analysis program (also available from the NSSDC) is used, the AGC voltage corresponding to the scaling of each X- and O-mode trace point is given as part of the output file with the extension .tra. On the full ionograms, which are available as binary files from the NSSDC, the range resolution is 0.025 ms (corresponding to a virtual-range resolution of 3.75 km) and three rows have zero video-output amplitude values; the middle row corresponds to the actual AGC value.
frequency of each scan line; in the swept-frequency portion of the ionogram they correspond to interpolated values between the frequency markers
Electron Gyrofrequency at time of ionogram frame sync