Capture Interval Research Articles

Track Map–Aided Capture of Virtual Balises: A Compatible Approach to Satellite-Based Railway Train Control

The use of a Global Navigation Satellite System (GNSS) is a significant requirement of next-generation railway train control systems. As one effective approach to integrate the GNSS positioning service into a train control system, the virtual balise (VB) solution makes it compatible with current system specifications and ensures the benefits in terms of cost efficiency and the autonomy of the train-borne subsystem. To create a VB system that performs normal balise functions, the standard VB solution suggests a capture interval (CI). However, a fixed CI cannot adapt to different train operating conditions, and thus, a full VB capture rate cannot at the same time be guaranteed with the desired spatiotemporal capturing accuracy level. In this study, a novel VB capture solution is proposed. The track map is involved in the VB capture to enable map matching of train location, interactive multiple model–based forward prediction of the next VB approaching status, and identification of the exact capture time. A field test of high-speed railway with accurately measured balises shows that the proposed approach can realize the full availability of VB capture without the difficulty of having to select a unique CI value. The capturing error and time offset are greatly reduced compared with the standard VB capture strategy using different CIs, which is significant for the future development and implementation of novel train control systems.

Use of the Lincoln Index Mark-Recapture Method to Estimate the Population Densities for Harvestable Yabbies, Cherax destructor, in Grow-Out Ponds

The Lin coln In dex mark-re cap ture method was eval u ated for its ac cu racy in es ti mat ing the num ber of harvestable yab bies, Cherax de struc tor, in earthen ponds. Where a sin gle re cap ture event was used to es ti mate the pop u la tion, a 3 to 6 day in ter val be tween the re lease and recap ture of marked an i mals tended to pro vide a more re li able es ti mate than a re lease and re cap ture in ter val of 24 hours. Where two re cap ture events were used to pro vide an av er age es ti mate, the method tended to un der es ti mate by 20% low den sity pop u la tions, that had been the sub ject of pre da tion by wa ter birds, whereas those es ti mates de ter mined f o r ponds with higher den si ties of cray fish, where avian piscivores were excluded, tended to be more ac cu rate (±10%). The ap pli ca tion of pop u la tion es ti ma tion as a tool for ar ti fi cial feed-man age ment is dis cussed.