If the lower altitude limit for the filter is the surface, where should the filter be set?

Setting the filter down to the surface level is the most appropriate choice when the lower altitude limit for the filter is specified as the surface. This means that the filter will be able to detect and process all radar returns from the ground level upwards, ensuring that no important returns just above the surface are missed.

In radar operation, particularly in areas where precise data is critical, such as in monitoring low-flying aircraft or distinguishing between ground and airborne objects, setting the filter to the surface level allows for increased sensitivity to those returns. This setting would effectively capture all objects in the lower altitude regime, which is crucial for accurate situational awareness.

In contrast, setting the filter above the surface level, even by a small margin, would result in the loss of valuable data, as any returns from the surface itself or very close to it would be filtered out. Similarly, a setting of 500 feet above the surface would introduce an additional layer of data loss, neglecting important information near the ground. Therefore, to maximize the radar’s effectiveness and ensure comprehensive detection capabilities, the filter should be configured down to the surface level.