Historical Bolide Infrasound Dataset (1960–1972)

Abstract

We present the first fully curated, publicly accessible archive of infrasonic records from ten large bolide events documented by the U.S. Air Force Technical Applications Center’s global microbarometer network between 1960 and 1972. Captured on analog strip-chart paper, these waveforms predate modern digital arrays and space-based sensors, making them a unique window on meteoroid activity in the mid-twentieth century. Prior studies drew important scientific conclusions from the records but released only limited artifacts, chiefly period–amplitude tables and unprocessed scans, leaving the underlying data inaccessible for independent study. The present release transforms those limited excerpts into a research-ready resource. By capturing ten large events in the mid-20th century, the dataset constitutes a critical reference point for assessing bolide activity before the advent of modern space-based and digital ground-based monitoring. The multi-year coverage and worldwide distribution of events provide a valuable reference for comparing past and more recent detections, facilitating assessments of long-term flux and the dynamics of acoustic wave propagation in Earth’s atmosphere. The dataset’s availability in a consolidated format ensures straightforward access to waveforms and derived measurements, supporting a wide range of scientific inquiries into bolide physics and infrasound monitoring. By preserving these historical acoustic observations, the collection maintains a significant record of mid-20th-century meteoroid entries. It thereby establishes a basis for further refinement of impact hazard evaluations, contributes to historical continuity in atmospheric observation, and enriches the study of meteoroid-generated infrasound signals on a global scale.

Dataset: DOI data identification number: 10.7910/DVN/VGSN7Q (direct URL to data: https://doi.org/10.7910/DVN/VGSN7Q).

Dataset License: CC-BY-NC

1. Summary

1.1. Background

This dataset was compiled to address a critical gap in observing small asteroids (meter- to tens-of-meter scale) and their associated atmospheric interactions. Between approximately 1960 and the early 1970s, multiple large bolides generated measurable infrasonic signatures, recorded by a global network of stations operated by the U.S. Air Force Technical Applications Center (AFTAC). [1] These acoustic-gravity waves document an era preceding extensive telescopic or satellite-based meteor observations, adding to the baseline of near-Earth object (NEO) influx data [2].

Previous analyses, e.g., [1,2], demonstrated that infrasonic records are effective for estimating meteoroid influx rates across a broad energy range (0.2–1100 kiloton of trinitrotoluene (TNT) equivalent, 1 kt TNT = 4.184 × 10¹² J). In particular, Silber et al. [2] digitized and reanalyzed the historical bolide infrasound records using modern techniques to further improve the flux rate estimates; however, that dataset has never been made available until now (see Section 2). The present dataset supports such methodologies by filling gaps in nuclear-surveillance-era observations and bridging them with modern campaigns. By making these historical acoustic measurements available, this article complements earlier research and situates the data for extended use in future studies on NEO detection, impact monitoring, and related atmospheric phenomena.

1.2. Value of the Data

• Long temporal span and global coverage: This dataset encompasses multiple bolide events documented from the early 1960s through to the mid-1970s, spanning different regions worldwide [2]. Such coverage includes infrasonic data from a range of meter-scale meteoroid entries recorded over more than a decade [1]. The resulting breadth of observations offers data points for many atmospheric conditions and impact scenarios during a period not well served by modern networks. By preserving scanned strip-chart paper recordings, these historic measurements exist as a distinct resource complementary to contemporary detection systems.
• Independent verification of historical impact energies and flux models: The waveforms, along with event timing and amplitude–period measurements, can be used to compute atmospheric energy depositions. The digitized records allow cross-checking of past impact energies derived from different observational methods, including satellite observations or optical techniques. Input from these acoustic waveforms can also inform refinements to meteoroid flux models by comparing recorded bolide frequencies and magnitudes to other data collected in the same era.
• Comparisons with modern infrasonic detection methods: Each event’s acoustic signature was recorded using analog equipment under operational conditions distinct from today’s networks. Modern, fully digital infrasonic array monitoring matured only several decades after the strip-chart records presented here, marking a methodological, rather than sharply chronological, transition [3]. By digitizing these historic signals, it becomes possible to compare frequency responses, signal-to-noise thresholds, and calibration standards. Such comparisons can illuminate shifts in detection efficiency over time, aid in upgrading current monitoring strategies, and enhance understanding of instrument performance differences between legacy analog apparatuses and contemporary infrasound sensor arrays.
• Applications in atmospheric acoustics, bolide energy calibration, and planetary science: Acoustic waveforms produced by bolides offer data on shock wave propagation under various atmospheric conditions. Period and amplitude measurements may be incorporated into broader research on atmospheric acoustics or serve as calibration references for other bolide observations. The dataset also supplies physical parameters relevant to planetary science topics, such as meteoroid fragmentation patterns or the influence of atmospheric composition on acoustic attenuation. This information has potential relevance for studies in planetary defense focused on impact risk.
• A historical baseline for detection capabilities: These records remain one of the earliest global collections of infrasonic signals from meter-scale asteroids. As a historical baseline, they document a window of bolide activity before widespread space-based or contemporary ground-based networks. This temporal depth helps refine flux estimates by comparing different observational periods, informing modern detection strategies, and guiding the interpretation of recent and future large-scale impacts.

2. Consolidated Historical Context and the Novelty of This Curated Release

Although the historic AFTAC bolide records have been analyzed in several peer-reviewed studies, most notably Revelle [1], ReVelle et al. [4], and Silber et al. [2], those papers concentrated on scientific interpretation rather than data dissemination (

Table 1. Comparison of data elements released by prior studies versus the present work. “Yes” indicates that the given element was publicly available through the cited publication or repository; “new” marks data products introduced in this article for the first time. Prior efforts provided only partial artifacts, manual measurements [1], and, in Silber et al. [2], raw unprocessed scans, whereas the current release consolidates those elements and adds cleaned and straightened images, calibrated waveforms, a digitized transfer function, overlay figures for validation, and comprehensive station metadata.

Data Element	Revelle [1]	ReVelle et al. [4]	Silber et al. [2]	This Work
Basic signal-measurement tables (period, amplitude)	yes (manually measured from paper charts)	yes	yes (measured from digitized records)	yes (consolidated [2])
Raw strip-chart scans (unaltered)	no	no	yes	yes
Cleaned scans (annotations/blemishes removed)	no	no	no	new
Straightened scans (curved pen paths rectified)	no	no	no	new
Calibrated pressure–time waveform files	no	no	no	new
Digitized instrument-response function (0.04–8.2 Hz)	no	no	no	new
Overlay figures comparing raw vs. digitized traces	no	no	no	new
Station coordinates	no	no	partial (7 stations)	new (13 stations)
Station names	no	no	no	new

). Consequently, only partial artifacts (signal-measurement tables and raw, unprocessed scans) ever entered the public domain. Silber et al. [2] originally hosted raw scans and measurement tables on an institutional server, which has since been decommissioned. In 2019, these same limited files were migrated to the Harvard Dataverse [5]. Until now, no cleaned images, straightened images, calibrated waveform files, or digitized instrument-response functions have been released, and the occasional in-text figures cannot substitute for a usable dataset. Table 1 contrasts the scope of those earlier releases with the data products provided here.

Our curated release delivers the complete research-ready package: high-resolution scans cleaned of all non-signal artifacts; geometrically straightened images that correct drum curvature; digitized, calibrated pressure–time waveform files for every station channel; a fully digitized 0.04–8.2 Hz transfer function; and overlay figures that juxtapose raw and processed traces for immediate validation. By extending the bare-bones raw scans into a FAIR-compliant archive, we enable reproducible reanalysis and new applications in atmospheric acoustics and meteoroid research. Here, we also include comprehensive station geographic coordinates and station names. This curated release therefore extends, rather than duplicates, the published literature and supports new investigations, such as re-evaluating bolide energy-scaling laws using modern techniques.

3. Data Description

This dataset comprises scanned images of original paper charts, digitized waveform files, and parameter tables for ten bolide events recorded worldwide between 1960 and 1972. No specialized software or proprietary code is needed to utilize these data; the scanned chart images open in any standard image viewer, and the parameter tables are stored in text-based or spreadsheet formats. Each event has a dedicated folder containing its images and digitized waveforms, making it straightforward to access and interpret the data (Figure 1).

The images for each event are organized into subfolders containing three principal data components:

i.

Raw scanned images (.tiff format), located within the subfolder named ‘raw’. These are high-resolution scans of the original strip-chart records, reflecting the condition in which the data were originally archived. In some cases, annotations, stamps, or marks appear on the charts, providing context but also occasionally obscuring the waveforms.

ii.

Cleaned images (.tiff format), located within the subfolder named ‘cleaned’. To improve clarity, each raw image has been subjected to an image-cleaning procedure that removed extraneous marks and annotations. This step improved the readability of the primary signal trace but preserved the critical waveform structures for downstream analysis.

iii.

Straightened images (.tiff format), located within the subfolder named ‘straight’. Because the pen recordings on some older strip charts were recorded cylindrically, many waveforms exhibit curved traces. These images have been corrected to a linear scale, except for those from 1971 and 1972, where the data were already captured digitally or did not require straightening.

The dataset’s digitized waveforms reside in a “waveforms” folder, offered in two main formats: plain text (.txt) and comma-separated values (.csv). Each .txt file contains data for a single station–channel pair, including the event date, physical units, and an indication of whether instrument-response corrections were applied. The two primary columns are time (in seconds) and amplitude (in pascals). Although the time vector is calibrated for its sampling rate (i.e., the spacing in seconds between samples), the start time for each record is set to zero rather than any specific absolute time reference. Consequently, these waveforms do not encode actual UTC timing or sensor-by-sensor offsets needed for beamforming or back-azimuth retrieval. In contrast, the .csv files compile all station–channel data for each bolide event, consolidating multiple digitized traces into a single spreadsheet. There are two sheets: one includes original time series, while the other one includes instrument corrected time series. To enable visual assessment, each event folder includes .png figures that overlay original (blue) and instrument-corrected (orange, also see Section 4) waveforms (see Figure 2) for all available stations and channels.

Finally, the dataset’s top directory contains the list of infrasound stations (and the associated metadata where available) and the summary tables (in both .xlsx and .txt formats) that list event details and detection metadata, such as station identifiers and measured signal characteristics. The list of 15 stations that detected infrasound signals from the bolides is included in the dataset. While the station two-letter codes are listed for all stations, the names and locations for two stations remain unavailable. For each waveform, primary parameters (i.e., peak-to-peak amplitude and the period at maximum amplitude) are extracted and tabulated. These measurements follow a standardized approach established in the earlier literature and related publications [1,2,6], ensuring consistency and comparability across events.

4. Experimental Design, Materials, and Methods

4.1. Spatiotemporal Context

This dataset originates from the systematic recording of atmospheric pressure fluctuations by infrasonic microbarometer stations operated under the U.S. Air Force Technical Applications Center (AFTAC) from the early 1960s through the mid-1970s [1,2]. Although these stations were developed primarily to detect and locate large-scale atmospheric nuclear explosions, their inherent sensitivity also made them capable of registering bolides: asteroids or meteoroids in the meter-to-tens-of-meters size range that produce shock waves upon entering Earth’s atmosphere. During the period in question, the nuclear-surveillance mission overshadowed “off-mission” detections such as incoming bolides. As a result, the infrasonic records generated by these events were not analyzed at the time.

As acoustic signatures corresponding to incoming asteroids became evident, Shoemaker and Lowery [7] first identified certain AFTAC waveforms as large bolides. Their observations represented a pivotal recognition that infrasonic detections could extend beyond nuclear test monitoring and into meteoroid events. Once these records underwent declassification, the dataset became broadly available for scientific investigation. Revelle [1] subsequently conducted a comprehensive study to quantify meteoroid influx rates, establishing these events as valuable historical observations of meter-scale objects entering Earth’s atmosphere. His analyses examined waveform characteristics, such as amplitude, period, and dominant frequency components, to illustrate the scientific potential of these once “off-mission” signals. In a subsequent study, Silber et al. (2009) [2] carried out a digitization process, converting the paper-based waveforms into numerical form, which allowed more accurate determinations of parameters such as peak-to-peak amplitude and period at maximum amplitude. Many details surrounding this historical evolution, and the context that motivated retrospective analysis of once-classified data, are discussed in Revelle [1].

Because the infrasonic network operated globally and spanned roughly a decade and a half, these records capture bolides that occurred at different times and in diverse geographic regions. Figure 3 provides an overview of their spatial distribution, whereas Table 2 lists each event’s date, time, and location. The recognized bolides took place between 1960 and 1972, illustrating the importance of historical sensor deployments in compiling long-term data on near-Earth objects. This dataset demonstrates how a network originally developed for a single, mission-specific purpose yielded broader scientific value once the non-nuclear infrasonic records, initially treated as ancillary, were re-evaluated. The resulting bolide detections thus serve as a valuable historical benchmark for studying near-Earth objects, their atmospheric interactions, and the extended utility of specialized sensor arrays beyond their primary operational scope.

Figure 3. Map showing the locations of the 10 large bolides.

Figure 3. Map showing the locations of the 10 large bolides.

Table 2. List of bolide events with dates, times, and locations [1].

Bolide Number	Date	Bolide Event Time [UTC]	Bolide Latitude [deg, N]	Bolide Longitude [deg, E]
1	2 Nov 1960	00:22	9.0	43.0
2	26 Sep 1962	15:45	30.0	35.0
3	27 Sep 1962	15:29	32.0	60.0
4	3 Aug 1963	16:45	−51.0	24.0
5	30 Nov 1964	03:10	18.0	−123.0
6	3 Jan 1965	21:51	21.0	68.0
7	1 Apr 1965	05:48	49.0	−117.0
8	12 Jun 1966	09:05	51.0	163.5
9	8 Jan 1971	18:26	30.0	40.0
10	14 Apr 1972	16:13	−13.0	78.0

Table 2. List of bolide events with dates, times, and locations [1].

Bolide Number	Date	Bolide Event Time [UTC]	Bolide Latitude [deg, N]	Bolide Longitude [deg, E]
1	2 Nov 1960	00:22	9.0	43.0
2	26 Sep 1962	15:45	30.0	35.0
3	27 Sep 1962	15:29	32.0	60.0
4	3 Aug 1963	16:45	−51.0	24.0
5	30 Nov 1964	03:10	18.0	−123.0
6	3 Jan 1965	21:51	21.0	68.0
7	1 Apr 1965	05:48	49.0	−117.0
8	12 Jun 1966	09:05	51.0	163.5
9	8 Jan 1971	18:26	30.0	40.0
10	14 Apr 1972	16:13	−13.0	78.0

4.2. Infrasound Network and Data Collection

At least 16 stations were in operation at any given time. Each infrasonic station consisted of an array of four or more microbarometers, spaced approximately 6–12 km apart. This spacing was originally chosen to triangulate sources of interest, primarily potential large-scale detonations, by comparing signal arrival times across the sensor array. However, comprehensive details regarding exact station locations, sensor deployments, and configuration changes remain unrecorded or unavailable.

The array design encompassed two principal passbands. A ‘high-frequency’ band covered 0.04–8.2 Hz, capturing impulsive signals typically associated with bolides or other rapid, large-scale explosions. A separate ‘low-frequency’ band, spanning 44–440 s, primarily contained atmospheric gravity waves (in the frequency domain, this corresponds to 0.002–0.023 Hz). The microbarometers themselves employed capacitance microphones coupled to Daniels-type ported-pipe filters, reducing local wind noise and improving the fidelity of detected atmospheric pressure fluctuations. Detailed technical specifications of these instruments have not been preserved or made available.

Continuous recording occurred via analog strip-chart paper, a standard technological approach of the mid-20th century. This system sometimes imparted geometric distortions to older records, such as curved pen trajectories, which were most prevalent prior to 1971. Real-time station operators often annotated these charts with handwritten notes or official stamps, indicating sudden excursions indicative of strong infrasound signals. Because the stations were optimized for nuclear-test detection, additional operational details, ranging from wind-pipe filter variations to station relocations and microphone replacements, were not systematically archived nor made available. Further to this, additional notes or any other relevant logs do not exist.

Sensitivity also varied among stations, shaped by local environmental conditions (e.g., wind turbulence) and minor calibration discrepancies. Although station-specific calibration data have not survived, a general response function suited to the broader AFTAC network was published by Flores and Vega [8]. This response, shown in Figure 4, serves as a practical transfer function across the 0.04–8.2 Hz range, enabling coherent interpretation of pressure signals recorded at multiple stations despite partial gaps in the original calibration records.

4.3. Data Preparation and Curation

Declassification of strip-chart records initially allowed the publication of fundamental wave properties derived from the original paper logs [1]. Later, these charts were scanned under the guidance of D. ReVelle and subsequently digitized by Silber et al. [2] to refine amplitude and period values for the ten bolide events. However, the complete set of these digitized records has not previously been released (see Table 1). The present data paper now makes available the full complement of raw and digitized datasets prepared by those earlier efforts, ensuring that both the original scanned images and the resulting numerical records appear together in a cohesive archival resource.

High-resolution scanning preserved critical markings, operator annotations, and any mechanical artifacts associated with the mid-century strip-chart system. Charts predating 1971 underwent geometric corrections to account for pen-curve distortions, followed by calibrated gain adjustments to retrieve amplitude data in pascals. Those steps yielded standardized digital waveforms, enabling the quantification of signal parameters (e.g., peak-to-peak amplitude, period at maximum amplitude) across multiple stations and channels. Representative examples of the scanned, cleaned, and “straightened” images appear in Figure 5. Only the high-frequency band was fully digitized for amplitude and period measurements, given that explosive atmospheric signals from bolides typically lie within that range. However, the low-frequency records (corresponding to 44–440 s periods) have also been scanned and cleaned, and are made available in this dataset, albeit without detailed digitization or derived signal parameters.

This integrated dataset, combining raw scans, corrected waveforms, and consistent metadata, ensures that historical bolide infrasound records are fully accessible to the broader community. It also provides a critical foundation for comparative analyses with contemporary bolide detections, thereby bridging decades of observational progress in meteoroid-infrasound research. For additional information on the final data products (e.g., amplitude or period tables), see also the Data Description Section.

5. Data Limitations

Despite the dataset’s unique value, several limitations warrant caution. First, some station documentation, including accurate geographic locations, array configurations, and calibration logs, is incomplete or missing, restricting the reliability of event localization and amplitude measurements. In particular, details of the wind-pipe filter designs are not available, complicating cross-station comparisons and limiting the ability to fully characterize each instrument’s response.

Second, this compilation does not include all bolide events that occurred during this time period. Detection thresholds, originally tailored to large-scale atmospheric signals, likely excluded smaller or higher-altitude bolides. Furthermore, it is unlikely that any cometary sources have been detected [1]. Consequently, any flux estimates derived from these data should be treated as conservative lower limits.

Lastly, the analog instrumentation of the 1960s and 1970s, although sophisticated for its time, introduces additional uncertainties. Strip-chart paper records often contain operator annotations or markings that obscure signal features, while manual archiving methods yield further inaccuracies in timing and amplitude calibration. Changes in sensor design or station relocation during the operational period remain undocumented, complicating comparisons across the network.

Nevertheless, this historically comprehensive dataset remains irreplaceable, providing a globally distributed, multi-year record of bolide activity that modern observations alone cannot replicate.