Late July break: ‘electric messages’ flying between two variations on summer
Across the wires the electric message came
He is no better. He is much the same.
— Alfred Austin, generally reckoned to be Britain’s worst Poet Laureate of all time, on the illness of the Prince of Wales in 1871
Nothing as gossip-worthy as that is travelling between the satellite dish on a tiled roof that could easily have been built in Gutenberg’s day — and an elongated expanse of semi-wilderness an ocean and oversized continent away. We might, if we only had the time to spare, tell a shaggy bat story — a four-day saga not quite over, starring the only known species of flying mammal. Never before have we kept company with a face copied often in medieval church gargoyles — yet oddly apt for its boffin-ish style of getting about.
Read these extracts from the Wikipedia entry on echolocation, and we defy you to come away less than one hundred per cent certain that bats are the ultimate geek totem animal:
FM signal advantages
The major advantage conferred by an FM signal is extremely precise range discrimination, or localization, of the target. J.A. Simmons demonstrated this effect with a series of elegant experiments that showed how bats using FM signals could distinguish between two separate targets even when the targets were less than half a millimeter apart. This amazing ability is due to the broadband sweep of the signal, which allows for better resolution of the time delay between the call and the returning echo, thereby improving the cross correlation of the two. Additionally, if harmonic frequencies are added to the FM signal, then this localization becomes even more precise.
CF signal advantages
The structure of a CF signal is adaptive in that it allows the CF-bat to detect both the velocity of a target, and the fluttering of a target’s wings as Doppler shifted frequencies. A Doppler shift is an alteration in sound wave frequency, and is produced in two relevant situations: when the bat and its target are moving relative to each other, and when the target’s wings are oscillating back and forth. CF-bats must compensate for Doppler shifts, lowering the frequency of their call in response to echoes of elevated frequency – this ensures that the returning echo remains at the frequency to which the ears of the bat are most finely tuned. The oscillation of a target’s wings also produces amplitude shifts, which gives a CF-bat additional help in distinguishing a flying target from a stationary one.