considered in detail photogrammetry, lidar, and IFSAR, which are all aerial mapping technologies using remote sensing in some form. The committee did not consider land-based surveying or land-based lidar, or measurement of bathymetric depth below water surfaces.

  1. Uncertainties in flood hydrology and hydraulics—uncertainty in floodplain maps arises in part from uncertainties in the framework map information, and in part from uncertainties in the computation of the discharge and elevation of floodwaters flowing through the landscape. The committee focused on issues related to map elevation data and not on other sources of uncertainty in flood risk assessment. A previous study examined uncertainty in flood hydrologic and hydraulic computations (NRC, 2000).

Besides the mapping technologies study presented in this report, FEMA has engaged the National Academies to undertake a longer-term flood map accuracy study within which the above issues will be addressed more fully.

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