| 12 | | * [http://fsf.nerc.ac.uk/] |
| | 13 | |
| | 14 | Please read the above guides as they cover the subject in much more detail than we can here. The following should give a brief summary of general "do's and don'ts", some of which may be obvious but are easy to forget when out in the field. |
| | 15 | |
| | 16 | * Do not stand between the sun and the survey point - you will cast a shadow over the area. Ideally stand as far back as possible so as not to create erroneous reflections. |
| | 17 | * Measure level, homogeneous targets of greater size than the resolution of the remote sensing data. In most cases this is not possible (even a square metre of concrete is not perfectly homogeneous) but try and find suitable targets. For example an expanse of car park may be suitable, a field of grass, a body of deep water. Surfaces that are not level will suffer greater from erroneous reflections (see bi-directional reflectance distribution fuinction (BRDF)). |
| | 18 | * Make sure you collect more than one observation over the target to improve the measurement statistics (get as many as possible). |
| | 19 | * Try to measure near the centre of the targets rather than the edge where possible. For example, if you survey a car park do not observe near the boundary fence or hedge. If observing a water body remember the depth of the bottom will also affect the reflectance (e.g. the shallow boundaries will be different to the deep centre). |
| | 20 | * Always get an accurate measurement of position (use GNSS / GPS connected to the measurement instrument). You may need to measure the same target for many seconds to get a more accurate position measurement. |
| | 21 | * Take photographs - they will act as a reminder to the conditions of the day and the targets surveyed. |
| | 22 | * Measure a mixture of targets - each target will have different spectral responses and you don't want to collect only targets with response in the VNIR (visible near infra-red) range if you are also interested in the SWIR (short wave infra-red). |
| | 23 | * Use calibrated targets - if you have these available and they are suitable for positioning over the airborne survey site (and suitable for the airborne instruments) then use them. |