Abstract: In a cloud height measuring device, the attenuation caused by deposits on the output and/or receiver windows of the device (e.g. by rain and/or dirt) are compensated for by measuring the degree of reflection of light from the window(s) when illuminated by light pulses. By means of a special measuring sequence in a processor unit included in the cloud height measuring device, light pulses separate from those used for the cloud height measurement itself, can be employed to assess the extent of the fouling. The measurement energy can then be controlled during the cloud height measurement proper, so that the total attenuation, caused by rain and dirt on the windows, is properly compensated for.

Abstract: A scrambling system for an audio frequency signal in which an audio signal is divided into blocks, each block being formed of a plurality of frames, the plurality of frames are rearranged on a timebase in a predetermined order at every block so as to be encoded and the encoded signal is re-arranged on the timebase in an original order so as to be decoded, in which there are provided a first signal processing circuit for inserting a redundant portion into a portion between adjoining frames and timebase-compressing the frames in response to the redundant portions upon encoding, a control signal generating circuit for inserting a control signal other than an audio information into the redundant portions, a control signal detecting circuit for detecting the control signal upon decoding and a second signal processing circuit for removing the redundant portions in synchronism with the detected control signal and timebase-expanding the frames in response to the redundant portions.