Saturday, June 21, 2014

CSA - Site Survey Method

If I were to say 'up' you can guarantee someone will say the complete opposite. Cell Site Analysis has this fascinating way of bringing opinion out of the woodwork an opposite response that hitherto such a response had remained hidden. The thought processes that make humans do this are far too complex to discuss in this thread and, frankly, would take a far greater mind than mine to offer to you an acceptable opinion. The best I can do is to offer to you some thoughts, evolved from knowledge skill and experience, and in doing so to invite you to enter the observation/opinion arena to see if you can offer improved solutions how to create a Site Survey Method.

The diagram below represents a sketch of the surrounding area where a murder has taken place. The first observation is that from knowledge the scene of crime is historic. Rarely does CSA come into play in live matters and if it does lawful interception elements are usually active, too. Thus, I am not considering overt, clandestine operations or montioring via bug phones etc.

Dependent on the information gathered during the Cell Site Identification procedure relating to the target area to be investigated, examiners should equip themselves with as much local information as is reasonable in order to conduct a site survey. It is most definitely worth the time and effort obtaining any aerial views that may be available, and that are up-to-date, about the target area.

Before visiting site, preparation is important. Attempt to gain some appreciation about the terrain, man-made clutter and natural form. Obtain local road maps to comprehend the road and street plan. Produce a rough
plan of the area that is to be inspected and approximately highlight those manmade structures that create landmarks.

Green Dotted Area
The diagram above depicts the area identified in the murder scenario discussed in the section on Neighbouring Cell Sites Identification. The localised scene is brought into view, the area identified, and dotted boundaries highlighted. The Red dotted boundary is the first areas in which an examiner may wish to conduct radio tests relevant to the immediate murder scene. Tests may need to be extended, as shown by the Green dotted boundary area.

During compilation of site information an examiner may wish to conduct a wider search so as to exclude other areas where the handset could detect Cells IDs (obtained during enquiries and mast tests) and other Cells d IDs detected by the test device handset. This is a good practice procedure and demonstrates the examiner is not assuming or excluding factors without due consideration. Quite often in criminal cases an
examiner will be instructed to survey a wider area due to information received, usually from a defendant suggesting his movements (Purple areas) at material times on the day of the crime, or an eyewitness thinks s/he sees the handset user at other locations. Always check them out and conduct radio tests.

Red Dotted Area
*Outdoor - Having selected the target zones for investigation, there is still the need to know how to conduct, in practical terms, those tests at the specific site. There are no defined guidelines that state measurements should be taken at certain distances. Experience suggests, considering the front, sides and rear of the block of flats (Fresnel), to select appropriate points of 1M near corners of buildings (denoted by the Green circled crosses) due to reflection or diffraction (e.g. Fresnel–Kirchhoff diffraction, Huygens–Fresnel diffraction etc) of radio signals.

Thereafter, select appropriate measurement points on a case by case basis at 1metres, 5metres, 10 metres or 100 metres (don't forget the increments inbetweeen) depending upon the length of the building and free land space surrounding it. The distance selected is optional, as already mentioned, but for the avoidance of doubt distances are suggested taking into account not only manmade objects, but, natural objects; such as trees or high hedges etc. Endeavour to take a camera to site so that photographs can be taken of all the places where measurements were actually conducted. As a place will represent a location, another useful tool for site surveys is a GPS monitor to identify precise coordinates, however it is best to avoid inferring GPS is part of the GSM or another cellular radio system as it is not the case.

Near-Wide Area Search
Whilst at the block of flats attempt to gain access to the roof and conduct tests, but equally as important is to get a visual bearing of the surrounding area. Take photographs (North-South-East-West) and tilt the camera to get overhead views of the clutter on the landscape surrounding the block of flats.

Finally, remember that where information is received about other locations where the handset user may have been (Purple areas). Identify each
location by using techniques adopted from Cell Site Identification and log of GPS monitor. Indoor and outdoor tests that are required should correspond to the information received.

In preparing this discussion a limited geographical/terrain location has been adopted merely to assist the flow of discussion. The information in this discussion should not be used as definitve for all geo/terrain profiles.

*Indoor will be discussed in another discussion thread .