Topside Ionogram Scaler With True Height Algorithm (TOPIST): Automated processing of ISIS topside ionograms

Abstract

The United States/Canadian ISIS‐1 and ISIS‐2 satellites collected several million topside ionograms in the 1960s and 1970s with a multinational network of ground stations that provided good global coverage. However, processing of these ionograms into electron density profiles required time‐consuming manual scaling of the traces from the analog ionograms, and as a result, only a few percent of the ionograms had been processed into electron density profiles. In recent years an effort began to digitize the analog recordings to prepare the ionograms for computerized analysis. As of November 2002, approximately 390,000 ISIS‐1 and ISIS‐2 digital topside‐sounder ionograms have been produced. The Topside Ionogram Scaler With True Height Algorithm (TOPIST) program was developed for the automated scaling of the echo traces and for the inversion of these traces into topside electron density profiles. The program is based on the techniques that have been successfully applied in the analysis of ground‐based Digisonde ionograms. The TOPIST software also includes an “editing option” for manual scaling of the more difficult ionograms, which could not be scaled during the automated TOPIST run. TOPIST is now successfully scaling ∼60% of the ISIS ionograms, and the electron density profiles are available through the online archive of the National Space Science Data Center at ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/isis/topside_sounder. This data restoration effort is producing a unique global database of topside electron densities over more than one solar cycle, which will be of particular importance for improvements of topside ionosphere models, especially the International Reference Ionosphere.

Statistical analysis of the ionization ledge in the equatorial ionosphere observed from topside sounder satellites

“…On the other hand, the ISIS-2 satellite was launched on April 1, 1971 into the circular polar orbit with the height of 1400 km and the inclination of 881 (Bilitza et al, 2004). Although the topside sounding of the ISIS-2 satellite provided analog data, a part of data has been converted into digital data by ISIS/ Alouette Topside Sounder Data Restoration Project (Bilitza et al, 2004). We used digital data archives provided by National Space Science Data Center (NSSDC).…”

“…The sounder echoes were received within the period of 22.22 ms. The resolution of the signal strength is 8 bits after conversion from analog data into digital form (Bilitza et al, 2004). To deduce the vertical plasma density profile, we adopted the parabolic in log N lamination method proposed by Jackson (1969).…”

Improvement of SuperDARN velocity measurements by estimating the index of refraction in the scattering region using interferometry

“…In addition to this, 23 2‐D profiles were also created with N e varying with latitude and altitude (only latitudinal horizontal gradients were considered in the present study). These 2‐D profiles were categorized as follows: (1) eight were based on ISIS II topside sounding measurements [ Bilitza et al , 2004]; (2) three were directly generated from the IRI model; (3) eight were based on midlatitude trough measurements [ Kersley et al , 1997; Moffett and Quegan , 1983]; (4) four were artificial profiles with exceptionally large horizontal gradients. An example of one of the 2‐D profiles is presented as Figure 1.…”

Modelling and observation of transionospheric propagation results from ISIS II in preparation for ePOP

“…First, orbital data of ISIS II had to be available for a particular pass. Second, it was necessary for the data from a pass to have been digitized (Bilitza et al, 2004). The digitized data from these passes were made available by the Alouette-ISIS Data Restoration project of the U.S. National Space Science Data Center (NSSDC, 2004).…”