For centuries, astronomers have rhapsodized about the music of

the spheres. Now an international group of architects, using modern

meteorological instruments, has designed and built a Keplerian harp. The

instrument converted the movement of clouds into the music of the heavens

at the Third Symposium for the Visual Arts last July in Amos, Quebec.

The Keplerian harp is named after German astronomer Johannes Kepler

(1571-1630), who first coined the expression "music of the spheres." Its

operating principle is based on compact-disc technology, in which a lens

captures tiny laser-beam modulations, and a decoding system converts them

into music or sound. The Keplerian harp reverses the process, projecting a

laser beam skyward so a telescope can capture the laser modulations produced

by the cloud cover. A MIDI musical interface is used in place of a decoding

system.

The project was headed by architect Nicolas Reeves, director of the NXI

Gestatio Design Lab based at the University of Quebec in Montreal. The

thorniest problem for this team of professional and student architects,

artists, computer specialists, and engineers was finding an integrated

laser/telescopic system. The answer was to obtain a lidar, a device similar

to a radar that emits pulsed laser light instead of microwaves.

The group rented a Vaisala CT12K cellometer lidar from Vaisala Inc. in

Woburn, Mass. Major airports and small airfields use this device to measure

the distance to the cloud base, which is critical for aviation safety. The

instrument emits pulsed light from a gallium-arsenide-diode laser; the light

is scattered by clouds and returned to a photodiode receiver. Each received

pulse is converted in real time to digital form, and a digital signal

processor determines cloud height by measuring the time taken for a light

pulse to be scattered from the cloud and returned to the ceilometer

receiver.

The Vaisala ceilometer was ideal for its new role as a music maker for

several reasons, according to Reeves, including a rugged design that keeps

the unit functioning accurately even during heavy rain or hail, so the

researchers can hear the music from thunderstorms and blizzards. The

standard connections of the CT12K make it easy to configure, and an output

serial port provides ASCII messages. Another benefit is the low-power pulsed

laser, which is easier to use than a regular beam.

With hardware in place, the Quebec designers turned to refining their

software. The CT12K delivers a message every 30 seconds. Each message

provides up to five or six numbers that can be converted to music, but about

8,000 numbers per minute are needed to make the simplest kind of music. In

addition, the inventors wanted their harp to play up to eight notes per

second, with each note requiring 20 parameters, such as volume, duration,

and tempo.

Reeves's crew solved the problem by reconstituting the cloud variations

between the messages, developing a simple fractal equation that enabled them

to produce the required amount of data after a few minutes of scanning. The

harp's operators can toggle between a cloud screen showing the lidar

information and a music screen displaying 16 windows, each window

corresponding to one channel. The software changes orchestrations

automatically to reflect different categories of cloud conditions, from

clear sky to complete cloud cover.

Each of the 16 channels plays one of 228 instruments. The designers divided

the operating range of the cellometer, up to 12,500 feet, into multiple

altitude ranges, each corresponding to a different instrumental section. For

example, 0 to 600 feet is for percussion, 400 to 1,000 feet for brass, 1,000

to 1,100 feet for timpani, and 1,000 to 2,000 feet for the violins and

cellos.

After hours of experimentation and fine-tuning, the Keplerian harp made its

successful debut at the July symposium, fascinating spectators. Reeves and

company are now seeking sponsors for a series of projects, such as the

installation of a visible laser beam near the lidar to show audiences where

the laser enters the cloud and thus "plays" it. They hope to incorporate

sounds from the harp's surroundings, including the voices of audience

members, into the harp's arrangements.

Their most ambitious dream is to include seven long-range, vertical

yttrium-arsenide-gallium lasers mounted at 65- to 160-foot intervals. The

visibly green beams crossing the sky should provide an unparalleled light

show to complement the symphony of the skies.