Summary

A successful small-format aerial photography (SFAP) survey requires planning of various issues, of which some may need to be prepared well ahead. This process is aided by good knowledge of the study site gained from personal experience, maps, satellite images and airphotos, and local colleagues.

For a given SFAP mission, both equipment and personnel must be available at the appropriate time of year under suitable weather conditions. This usually requires some travel for the involved people and shipment of necessary equipment, which may prove difficult for international missions. The accessibility of the site by automobile or boat as well as for the survey personnel on foot can be an important consideration when choosing the survey system, as some sites like wetlands, nature reserves, or rugged terrain can be impossible or difficult to enter and navigate on the ground. Site characteristics—obstacles, topography, lighting, wind—also may influence field procedures. High-altitude SFAP presents special circumstances because of thin air and alpine weather effects.

For all applications that involve measuring and mapping, ground control for georeferencing and geometric correction of the images is necessary. Given the large scale of SFAP images, measuring coordinates of the ground control points (GCPs) would usually require the high accuracies of a terrestric survey by total station. Temporary GCPs are sufficient for one-time surveys; permanent GCPs need to be installed for long-term monitoring purposes. Careful targeting with colors that contrast well with the surrounding area helps to identify the GCPs in the photographs.

Although most SFAP platforms are not navigable precisely, some basic air survey calculations should be an integral part of any mission planning in order to ensure the best possible imagery for the intended application. Target flying heights can be calculated prior to the survey for the desired area coverage or ground sample distance (pixel resolution), and the possibilities of achieving stereoscopic coverage can be assessed for a given platform and camera system. Such calculations can help to assess if the desired image characteristics can be realized with the existing equipment and which compromises or adaptations could be necessary.

Legal constraints of aviation laws may apply for SFAP depending on the country, the platform used, and the mission purpose. Permission to conduct SFAP may require authorizations from various governmental agencies as well as insurance policies, and careful review of the individual country's body of laws and the details of insurance policies is highly recommended. The help of local informants is most useful in situations that may be unfamiliar to the photographer. The best approach is to utilize an SFAP system that is robust, easy to transport, supported by available personnel and supplies, and capable of acquiring suitable imagery within the local legal framework.

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