In modern armed conflicts, civilian population centers, infrastructure, and humanitarian corridors are frequently subjected to indiscriminate artillery shelling, rocket barrages, and precision airstrikes. In the immediate aftermath, belligerent parties invariably trade accusations, claiming strikes originated from hostile territory, represented misfired defense interceptors, or were staged entirely.

For human rights investigators, conflict monitors, and open-source intelligence (OSINT) researchers, the physical impact crater left by an explosive projectile serves as a permanent, measurable ballistic compass.

By analyzing the physical morphology of the impact crater, the geometry of surrounding fragmentation spray, and the soil ejecta pattern, investigators can mathematically establish the Angle of Arrival (AoA), calculate the compass bearing to the firing battery, and determine the class of munition deployed.

This field manual details the physical principles of crater analysis, standard field measurement workflows, and the geometric trigonometry required to document artillery strikes with forensic defensibility.

1. Principles of Terminal Ballistics and Crater Mechanics

When a high-explosive artillery shell (such as a 122mm, 152mm, or 155mm projectile) strikes the earth, its terminal velocity (typically 200 to 800 m/s) and angle of fall dictate the physical interaction between the kinetic casing and the ground substrate.

                    TERMINAL FLIGHT PATH (ANGLE OF FALL θ)
                                     \
                                      \  PROJECTILE CASING
                                       \
════════════════════════════════════════▼════════════════════════════════
             [DIRECTION OF FIRE]       * DETONATION POINT
                                    /     \
                                   /       \
                     SOIL UPTHRUST         CRATER BASIN & EJECTA CONE

The Three Blast Regimes: Fuze Settings

The physical geometry of a crater depends fundamentally on the fuze mechanism selected by the firing crew:

1. Super-Quick / Point Detonating (PD): Detonates instantaneously upon initial physical impact. Leaves a shallow, broad dish-shaped depression with an extensive, highly legible radial fragmentation spray (“butterfly” pattern) on the surface. Ideal for direction-of-fire analysis.
2. Delay Fuze: Projectile penetrates 0.5 to 2.0 meters into the soil, pavement, or concrete roof slab before high-order detonation. Generates a deep, conical crater with steep walls and extensive upward soil displacement (ejecta lip), but reduced surface shrapnel scarring.
3. Proximity / Airburst (VT): Detonates radar-altimeter-controlled 3 to 10 meters above the terrain. Produces no physical crater whatsoever, but coats the ground with an intense, omnidirectional shower of downward-angled fragmentation pitting.

2. Reading the Crater: Determining the Direction of Origin

A common misconception among untrained observers is that explosive shrapnel spreads outward in a simple circle. In terminal ballistics, projectile momentum forces shrapnel and soil outward in highly asymmetric, mathematically predictable patterns.

                             TOP-DOWN CRATER GEOMETRY
                        (Direction of Fire: Top to Bottom)

                             [FIRING BATTERY POSITION]
                                        ▲
                                        │
                                 ORIGIN BEARING
                                        │
                                  ┌─────┴─────┐
                                  │   ENTRY   │  <-- Shallow entry slope
                             ┌────┴───────────┴────┐
                             │                     │
                    SHRAPNEL │    CENTRAL BASIN    │ SHRAPNEL
                    "SIDE-   │    (DETONATION)     │ "SIDE-
                    SPRAY"   │                     │ SPRAY"
                             └────┬───────────┬────┘
                                  │   LIP /   │  <-- Steep upthrust lip /
                                  │  EJECTA   │      heavy forward debris
                                  └───────────┘

The Shrapnel “Butterfly” / Bowtie Pattern

As the projectile detonates while traveling forward at high velocity, the cylindrical steel casing breaks into thousands of razor-sharp fragments. * Due to forward kinetic vector summation, fragments from the sides of the casing are thrown laterally and slightly forward at an angle of roughly $60^\circ \text{ to } 85^\circ$ to the flight axis. * Very little shrapnel travels directly backward along the flight path. * This produces a distinctive “bowtie” or “butterfly” spray of etched shrapnel lines on asphalt, masonry, or soil flanking the sides of the crater. * The Direction Rule: The bisector line running perpendicular to the lateral shrapnel wings points directly back along the flight path toward the firing battery.

Soil Ejecta and Undercut Lips

In soil and unpaved terrain: * The side of the crater closest to the firing weapon has a shallow, gradual slope where the projectile entered the ground. * The side of the crater furthest from the firing weapon features a sharp, near-vertical under-cut wall and a heavy crest of displaced soil (the terminal lip or ejecta tongue), pushed forward by the projectile’s terminal kinetic momentum.

3. Step-by-Step Field Measurement Methodology

When documenting a strike site in the field or analyzing high-resolution eyewitness photographs and drone footage, follow a standardized 5-step investigative protocol:

[1. CLEARING & SAFETY] ──► [2. CENTER AXIS] ──► [3. COMPASS BEARING] ──► [4. SOIL EXCAVATION] ──► [5. FRAGMENT AUDIT]

Step 1: Establish Scale and Photographic Reference

Photograph the crater from at least four orthogonal angles (North, South, East, West) with a metric scale bar or standard object of known dimension placed at the crater rim. Take perpendicular overhead drone or elevated pole shots to capture the entire shrapnel field.

Step 2: Lay the Centerline Axis

Place a surveyor’s cord across the center of the crater: 1. Align the cord with the center of the shallow entry slope and the center of the primary ejecta lip. 2. Align the cord symmetrically between the left and right wings of the shrapnel bowtie spray. 3. This cord represents the Line of Arrival (LoA).

Step 3: Measure Magnetic Azimuth and Correct for Declination

Using a sighting prismatic compass or calibrated digital inclinometer: * Sight along the Line of Arrival cord pointing away from the ejecta lip back toward the entry side. * Record the magnetic azimuth in degrees ($0^\circ \text{ to } 360^\circ$). * Convert magnetic azimuth to True Geodetic Azimuth using the geographic location’s current magnetic declination: $$\text{Azimuth}{\text{true}} = \text{Azimuth}$$}} + \text{Declination

Step 4: Excavate the Fuse Furrow

Carefully remove loose debris from the base of the crater. In many artillery and rocket strikes, the solid hardened steel nose fuze survives the blast intact and buries itself into the subsoil at the deepest point of the crater: * The angle at which the fuze is lodged in the bedrock reveals the terminal angle of impact ($\theta$). * Measure this angle using a digital protractor against the horizontal plane.

5. Reverse Triangulation: Mapping Candidate Battery Positions

Once the True Azimuth back to the firing source is established, investigators cannot simply draw an infinite line across a satellite map. The line must be constrained by the minimum and maximum ballistic ranges of candidate weapons systems.

[TARGET CRATER] ═════════════════════════════════════════════════════════════════════►
       │
       ├─- 0 km to 4 km: Mortar Danger Envelope (60mm, 82mm, 120mm)
       │
       ├─- 4 km to 15 km: Rocket Artillery Minimums (122mm Grad) & Light Howitzers
       │
       ├─- 15 km to 30 km: Standard Tube Artillery Envelope (152mm 2S19 / 155mm M777)
       │
       └─- 30 km to 70+ km: Long-Range Rocket Systems (220mm Uragan, 300mm Smerch, HIMARS)

Identifying Munition Class from Crater Metrics

The physical volume of the crater provides initial bounding parameters:

Cross-Referencing Frontline Trench Lines and Radar Passes

1. Draw the calculated azimuth bearing line onto Sentinel-2 multispectral imagery or high-resolution satellite base maps.
2. Intersect the bearing line with verified troop disposition lines (e.g., active defense lines, known trench complexes, fortified tree-lines).
3. Query NASA FIRMS thermal anomaly data for that exact strike date along the corridor to detect heat signatures from artillery battery launches.

6. Preserving Ballistic Debris for Judicial Accountability

Crater analysis findings are central to war crimes investigations submitted to international bodies (such as the International Criminal Court):

• Preserve Munition Fragments: Collect and photograph base plates, rifling driving bands (gilding metal rings imprinted with artillery tube grooves), and fuze nose cones.
• Document Serial Numbers and Factory Stamps: Cyrillic, NATO, or Chinese Cyrillic lot numbers on fragment scrapings establish exact manufacturing batches and supply chains.
• Geotagged Video Verification: Record unbroken video panning from the crater basin to the horizon, demonstrating geographic landmarks to prevent claims of digital manipulation.

By grounding conflict reporting in terminal ballistics and geometric trigonometry, researchers convert transient warzone destruction into undeniable legal evidence.