The open-source investigation team Bellingcat released a new report on Russian cross-border artillery strikes in Ukraine in the summer of 2014. According to the report, the Russian Armed Forces fired on targets in Ukraine "at least 149 times." An additional 130 locations have been identified as "likely to have been used" as artillery positions.
Based on analysis of shell craters, Bellingcat claims that "thousands of artillery projectiles were fired by the Russian military on targets inside Ukraine in the summer of 2014." The report also says that cross border artillery attacks began in early July 2014 and increased in frequency and scale into August and September.
The report's authors surveyed 2,254 potential sites within 22 km of the Russian-Ukrainian border, based on the approximate maximum range of a 122mm howitzer. Of that, 1,344 sites were found to be not relevant to the investigation, while 518 sites were found to be artillery strikes from inside Ukraine. Each potential firing position was classified by two analysts. A site could be classified as a "likely firing position" only if both analysts agreed.
Likely firing positions were classified based on the type of artillery used. For example, Multiple Launch Rocket Systems (MLRS) such as the BM-21 Grad and BM-30 Smerch leave blast marks on the ground which reveal their position and the direction of fire. In the case of howitzer firing sites, signs like vehicle track marks and dug-in firing positions were used.