Integration of Historical and Modern Gravimetric Data to Model the Temporal Variation of the Gravity Field over Italy

This study is part of a broader effort to modernize the Italian gravimetric database and to support the computation of the new national geoid. Its primary aim is the integration of historical gravimetric measurements with modern observations, including data from ongoing airborne surveys, to establish a consistent framework for analyzing temporal variations of the gravity field across Italy. The current study addresses the initial phase of this effort, including the digitization of historical records, the transformation of legacy coordinates into the official Italian geodetic reference frame, a preliminary GIS-based visualization, and the design of a unified database for future spatial and temporal analyses.

Historical gravimetric records from major volumes edited by the former Italian Geodetic Commission (Ballarin, 1936; Cunietti & Inghilleri, 1955; Riccò, 1903; Solaini, 1939; Soler, 1930), covering the late 19th century to the 1960s, were digitized. Pages were scanned at high resolution, and image enhancement techniques, including noise reduction, contrast adjustment, and edge sharpening, were applied to improve legibility and data extraction.

Digitization employed AI-based optical character recognition (OCR) using DeepSeek OCR (Wei et al., 2025), supported by ChatGPT-4 and ChatGPT-5 (OpenAI, 2023, 2025) for table-structure interpretation. This workflow enabled accurate recognition of degraded or complex tables, merged cells, and inconsistent delimiters. Data were initially stored in editable Excel spreadsheets as an intermediate validation step to verify, correct, and standardize key parameters, including geographic coordinates, orthometric height, absolute gravity measurements, year of observation, and survey campaign information. Historical coordinates referred to old Italian datums (Roma1940, ED1950, or other local datums) were converted to WGS84 (EPSG:4326) to ensure compatibility with modern measurements. A key challenge stemmed from the heterogeneity of the legacy reference frame, which required accurate datum transformations for reliable integration with contemporary datasets.

Following digitization and coordinate conversion, historical data are being prepared for integration with modern gravimetric measurements from the national network and ongoing airborne surveys. Initial GIS-based visualization provides an early assessment of spatial coverage and potential inconsistencies. The unified database is designed to manage spatial variability and temporal evolution of gravity and is scalable to accommodate future datasets.

Once fully established, the dataset will undergo quality control and validation using statistical and geospatial methods. While temporal gravity modeling lies beyond the scope of this contribution, the proposed workflow lays a solid foundation for subsequent analyses.

References

Ballarin, S., 1936: Trentadue determinazioni di gravità relativa. Commissione geodetica italiana.

Cunietti, M., Inghilleri, G., 1955: Rete Gravimetrica Fondamentale Italiana. Commissione geodetica italiana.

OpenAI. 2023. GPT‑4 Technical Report: https://cdn.openai.com/papers/gpt-4.pdf.

OpenAI. 2025. GPT‑5 System Card (Technical Overview): https://cdn.openai.com/gpt-5-system-card.pd

Riccò, A., 1903: Determinazione della Gravità Relativa in 43 Luoghi della Sicilia Orientale delle Calabrie. Memorie della Società Degli Spettroscopisti Italiani.

Soler, E., 1930: Due Campagne Gravimetriche sul Carso. Università di Padova.

Solaini, L., 1939: Determinazione di gravità relativa eseguite a Castelnuovo Scrivia, Tortona, Alessandria, Valmadonna, S. Salvatore Monferrato e Sannazzaro De' Burgondi nell'anno 1939. Commissione geodetica italiana.

Wei, H., Sun, Y., Li, Y. . DeepSeek-OCR: Contexts Optical Compress