Reprocessing receiver data

Why reprocess receiver data

Detection data is regularly reprocessed (also referred to as "rerun") following the initial upload and processing. This is primarily required to account for changes in metadata. As described here, proper metadata management is essential for identifying tags, in particular Lotek tags.

Put simply, if a tag does not does have an active deployment at the time the receiver data was originally processed that covers the period of the detection, that tag will not be among the candidate tags that the tagfinder algorithm has at its disposal when attempting to match raw data with known tags. In other words, your tag will not be detected.

Sometimes even despite best efforts, tag metadata is either not present or not correct when detection data is first processed. This makes repeated reprocessing of receiver data a necessity.

There is no fixed schedule as to how often receivers are rerun, but typically it is within the first 1-2 months of first upload, then roughly every 3 months to 6 months after that, decreasing in frequency as more time has elapsed since when it was first recorded and processed

Why detections can sometimes appear or change after reprocessing

Though receiver reprocessing is unavoidable given the constraints of the current technology, it can lead to some surprising results, primarily when detections that were previously seen disappear entirely, or are changed to different tags.

Detections don't appear after first upload but do appear after reprocessing

This is the most common and straightforward case. Usually it is a matter of researchers forgetting to update their tag metadata prior to uploading a station's data. It's also more likely to occur when deploying tags near internet-connected stations, as they often upload data before the updated metadata is present in the system.

This is the most common answer to the question of why no detections are showing up despite having tagged in the near vicinity of an active station.

Detections change to different tags after reprocessing

In this case, rather than there being no candidate tags whatsoever that might match the raw data, as in the previous case, there are tags with active deployments that are potential candidate tags. Due to the allowed tolerance of tag signal properties, sometimes a less suitable candidate tag is selected by tagfinder if the more suitable one is unavailable. Once the proper tag metadata has been updated and the receiver reprocessed, it will resolve to the correct tag.

Detections that did appear then later disappear

This is not directly related to receiver reprocessing, but worth describing here along with the other cases. This is when detections are later identified as false positives, either related to aliasing or a noise event, and are flagged in the database. Flagging them will remove them from all the the detection summaries on Motus.org, but not the complete data downloaded with the R package, where the runs and hits will be assigned the value of motusFilter == 1 . Read more about that here.