Altitude-dependent absorbed dose rate profiles encountered by the (H₂O-based) ICRU phantom (solid black line), the Venusian air (solid blue line), and a microbial cell (solid red line). Also shown are the relative differences with respect to the ICRU sphere, displayed as dashed lines. For the dose in the air plot (blue line), the relative difference includes dotted lines that correspond to maximum and minimum differences, as described in detail in thetext.