Understanding the spectral properties of sources is crucial for the characterization of the radio source population. In this work, we have extensively studied the ELAIS N1 field using various low-frequency radio observations. For the first time, we present the 1250 MHz observations of the field using the upgraded Giant Meterwave Radio Telescope (uGMRT) that reach a central off-source RMS noise of ∼12 μJy/beam. A source catalogue of 1086 sources is compiled at 5 sigma threshold (>60μJy) to derive the normalized differential source counts at this frequency that is consistent with existing observations and simulations. We present the spectral indices derived in two ways; two-point spectral indices and by fitting a power-law. The latter yielded a median α=−0.57±0.14, and we identified nine ultra-steep spectrum sources using these spectral indices. Further, using a radio colour diagram, we identify the three mega-hertz peaked spectrum (MPS) sources, while three other MPS sources are identified from the visual inspection of the spectra, the properties of which are discussed. In our study of the classified sources in the ELAIS N1 field, we present the relationship between α and z. We find no evidence of an inverse correlation between these two quantities and suggest that the nature of the radio spectrum remains independent of the large-scale properties of the galaxies that vary with redshifts.

The low-latitude ionosphere is a dynamic region with a wide range of disturbances in temporal and spatial scales. The Giant Metrewave Radio Telescope (GMRT) situated in the low-latitude region has demonstrated its ability to detect various ionospheric phenomena. It can detect total electron content (TEC) variation with precision of 1.0 mTECU and also can measure TEC gradient with an accuracy of about 0.7 mTECU/km. This paper describes the spectral analysis of previously calculated TEC gradient measurements and validates them by comparing their properties using two bands. The analysis tracked individual waves associated with medium-scale traveling ionospheric disturbances (MSTIDs) and smaller waves down to wavelengths of ∼10 km. The ionosphere is found to have unanticipated changes during sunrise hours, with waves changed propagation direction as the sun approached the zenith. Equatorial spread F disturbances during sunrise hours is observed, along with smaller structures moving in the same direction.

The Earth’s ionosphere introduces systematic effects that limit the performance of a radio interferometer at low frequencies (≲ 1 GHz). These effects become more pronounced for severe geomagnetic activities or observations involving longer baselines of the interferometer. The uGMRT, a pathfinder for the Square Kilometre Array (SKA), is located in between the northern crest of the Equatorial Ionisation Anomaly (EIA) and the magnetic equator. Hence, this telescope is more prone to severe ionospheric conditions and is a unique radio interferometer for studying the ionosphere. Here, we present 235 MHz observations with the GMRT, showing significant ionospheric activities over a solar minimum. In this work, we have characterised the ionospheric disturbances observed with the GMRT and compared them with ionospheric studies and observations with other telescopes like the VLA, MWA and LOFAR situated at different magnetic latitudes. We have estimated the ionospheric total electron content (TEC) gradient over the full GMRT array which shows an order of magnitude higher sensitivity compared to the Global Navigation Satellite System (GNSS). Furthermore, this article uses the ionospheric characteristics estimated from the observations with uGMRT, VLA, LOFAR and MWA to forecast the effects on the low-frequency observations with the SKA1-MID and SKA1-LOW in future.

Radio interferometers, which are designed to observe astrophysical objects in the universe, can also be used to study the Earth’s ionosphere. Radio interferometers like the Giant Metrewave Radio Telescope (GMRT) detect variations in ionospheric total electron content (TEC) on a much wider spatial scale at a relatively higher sensitivity than traditional ionospheric probes like the Global Navigation Satellite System (GNSS). The hybrid configuration of the GMRT (compact core and extended arms) and its geographical location make this interferometer an excellent candidate to explore the sensitive regions between the northern crest of the Equatorial Ionization Anomaly (EIA) and the magnetic equator. For this work, a bright radio source, 3C 68.2, is observed from post-midnight to post-sunrise (∼ 9 h) to study the ionospheric activities at solar-minima. This study presents data reduction and processing techniques to measure differential TEC (⁠δTEC⁠) between the set of antennas with an accuracy of 1.0 mTECU. Furthermore, using these δTEC measurements, we have demonstrated techniques to compute the TEC gradient over the full array and micro-scale variation in 2D TEC gradient surface. These variations are well equipped to probe ionospheric plasma, especially during the night-time. Our study, for the first time, reports the capability of the GMRT to detect ionospheric activities. Our result validates, compared to previous studies with VLA, LOFAR, and MWA, the ionosphere over the GMRT is more active, which is expected due to its location near the magnetic equator.