From sti at ictp.it  Mon May  4 09:02:34 2026
From: sti at ictp.it (Science, Technology and Innovation)
Date: Mon, 4 May 2026 09:02:34 +0200
Subject: STI Seminar - Tuesday, 5 May at 11h00 "Spatio-temporal variabilities
 of ionospheric features observed using University of Calcutta VHF
 Radar and GNSS receivers: Case studies and modeling " by Ashik PAUL
Message-ID: <691f058c-1025-4659-ad7b-e67d5637ef10@ictp.it>

Dear All,

On Tuesday, 5 May? at 11:00 CET,? Ashik Paul (University of Calcutta) 
will give a seminar titled:

*"Spatio-temporal variabilities of ionospheric features observed using 
University of Calcutta VHF Radar and GNSS receivers: Case studies and 
modeling "

*Abstract:

Equatorial ionospheric irregularities intersect and interfere with 
transionospheric radio signals often resulting in serious degradation of 
their performance including that of satellite-based systems and 
services. While such phenomena are associated with geomagnetic disturbed 
conditions in the mid and high latitudes, they could occur even under 
geomagnetic quiet conditions in the equatorial and low latitudes. The 
radio frequency signals affected also varies across a wide spectrum 
extending from VHF to L-band and often S-band as well. Some novel 
coordinated experimental observations were recorded during 
February-March 2024 using University of Calcutta VHF radar (CUVR) 
operating at 53 MHz at the Ionosphere Field Station, Haringhata 
(22.93?N, 88.37?E geographic; 35?N magnetic dip) and GPS L-band 
measurements from North Bengal University (NBU) (26.71?N, 88.35?E 
geographic; 42?N magnetic dip). On March 18, 2024, the VHF radar 
backscattered signals noted a number of irregularity patches over a 
common ionospheric volume with the GPS observations from NBU 
more-or-less around the same $me interval. Similar analyses have also 
been done for other dates in February and March 2024. These novel 
coordinated measurements validate the simultaneous coexistence of 
ionospheric irregularities of varying scale sizes ranging from 
centimetres to metres using the VHF radar and GPS. However, an 
outstanding issue to consider is the occurrence of ionospheric 
irregularities even at L-band at a magnetic dip of 40?N during late 
evening and midnight hours. This brings forth the question whether these 
irregularities could be attributed to equatorial plasma bubbles or to 
some remnants of transitional mid- latitude plasma density structures. 
This coordinated approach offers a comprehensive understanding of the 
spatial and temporal characteristics of these phenomena, which are 
critical for improving communication and navigation systems in the 
low-latitude region. Some of the background low-latitude ionospheric 
features were measured using the MEDEA receiver operational at the 
Institute of Radio Physics and Electronics (IRPE), University of 
Calcutta as part of the ESA AMIC project, which exhibited depletions in 
Total Electron Content (TEC) associated with the occurrence of 
ionospheric irregularities. However, in order to demonstrate the 
day-to-day variabilities of the occurrence of irregularities, 
ionospheric reconstruction using GNSS data was used. This technique 
requires accurate measurement of TEC which may be provided from a 
reliable model. Accurate short-term prediction of ionospheric TEC is 
essential for mitigating positioning errors in GNSS, particularly over 
low-latitude regions characterized by strong nonlinear variability. This 
study proposes HTR- X++, a physics-informed hybrid deep ensemble 
framework that integrates temporal deep learning with gradient-boosted 
regression. The model supports multi-horizon forecasting (1-hour and 
3-hour ahead) and incorporates thermospheric composition (O/N2) to 
account for ionosphere?thermosphere coupling. The framework is evaluated 
using GNSS-derived TEC data from IRPE across contrasting seasonal 
regimes and further validated at an independent station NBU. Results 
demonstrate substantial improvement over persistence baselines, 
achieving up to ~40% reduction in RMSE and correlation values 
approaching unity (R ? 0.98?0.99). These results establish HTR-X++ as a 
robust, interpretable, and operationally viable framework for real-time 
TEC forecasting.


Speaker:
 ? ? Ashik Paul - Institute of Radio Physics and Electronics University 
of Calcutta, India

Indico: https://indico.ictp.it/event/11339/

The seminar will take place at the Marconi Lab, E. Fermi building (Via 
Beirut, 6).

You are all most welcome to attend!

Best regards,

Erica

Erica Sarnataro
Secretariat
Science, Technology and Innovation
The Abdus Salam International Centre for Theoretical Physics (ICTP)
Trieste,  Italy
Tel. +39-040-22404623 (NEW PHONE NUMBER)
www.ictp.it/research/sti.aspx
e-mail:sti at ictp.it