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A system for measuring properties of a medium includes an electromagnetic generator for forming a CW carrier, a digital encoder for forming a digital message, and a modulator for modulating the CW carrier with the digital message to form a digitally modulated CW carrier. The medium provides a channe

A system for measuring properties of a medium includes an electromagnetic generator for forming a CW carrier, a digital encoder for forming a digital message, and a modulator for modulating the CW carrier with the digital message to form a digitally modulated CW carrier. The medium provides a channel for propagating the digitally modulated CW carrier. The system further includes a receiver configured to receive the propagated, digitally modulated CW carrier, and a processor for measuring at least one property of the medium. The medium may be disposed within a gaseous atmosphere, a body of water, or a cell of a laboratory.

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What is claimed: 1. A system for chemical identification of a medium comprising: a laser for generating a CW carrier, a digital encoder for forming an encoded word, an electro-optic (EO) modulator for modulating the CW carrier with the encoded word to form an encoded CW carrier, a medium for propag

What is claimed: 1. A system for chemical identification of a medium comprising: a laser for generating a CW carrier, a digital encoder for forming an encoded word, an electro-optic (EO) modulator for modulating the CW carrier with the encoded word to form an encoded CW carrier, a medium for propagating the encoded CW carrier, a receiver configured to detect the propagated, encoded CW carrier to form a detected signal, a processor configured to measure bit error rate (BER) of the detected signal and a wavelength controller, coupled to the laser, for modifying a wavelength of the CW carrier, wherein the medium includes an absorption line, the wavelength controller is configured to modify the wavelength of the CW carrier by scanning about the absorption line, and the processor is configured to identify the medium based on an increase in the BER of the detected signal at the absorption line. 2. The system of claim 1 wherein the encoded CW carrier includes an encoded binary phase shift keyed (BPSK) word, an encoded binary frequency shift keyed (BFSK) word, or a differential phase shift keyed (DPSK) word. 3. The system of claim 1 wherein the medium is disposed within a gaseous atmosphere, a body of water, or a cell of a laboratory. 4. The system of claim 1 wherein the processor includes dual digital matched filters (DMFs) for reconstructing, on a bit-by-bit basis, the detected signal to form a received message word. 5. The system of claim 1 wherein the processor includes a bit error accumulator for comparing, on a bit-by-bit basis, the encoded word formed by the digital encoder with the detected signal and accumulating bit errors based on the comparison. 6. The system of claim 1 wherein the digital encoder is configured to form a pseudonoise (PN) encoded word. 7. The system of claim 1 wherein the digital encoder forms a plurality of identically encoded words, the modulator modulates the CW carrier with the plurality of identically encoded words, the receiver forms the detected signal based on the plurality of identically encoded words, and the processor measures the BER of the detected signal based on the plurality of identically encoded words. 8. A system for measuring properties of a medium comprising: an electromagnetic generator for forming a CW carrier, a digital encoder for forming a digital message, a modulator for modulating the CW carrier with the digital message to form a digitally modulated CW carrier, a medium for providing a channel for propagating the digitally modulated CW carrier, and a receiver configured to receive the propagated, digitally modulated CW carrier, wherein the receiver includes a processor configured to measure bit error rate (BER) of the medium. the receiver is set to detect a signal-to-noise ratio (SNR), in which a relatively small change of SNR provides a relatively large change in bit error probability of the received, digitally modulated CW carrier, and the processor is configured to identify the medium based on the measured BER wherein the medium is characterized by a relatively small change of SNR providing a relatively lame change in bit error probability. 9. The system of claim 8 wherein the medium is disposed within a gaseous atmosphere, a body of water, or a cell of a laboratory. 10. The system of claim 8 wherein the electromagnetic generator includes a distributed feedback laser. 11. The system of claim 8 wherein the digital message includes an encoded binary phase shift keyed (BPSK) word, an encoded binary frequency shift keyed (BFSK) word, or a differential phase shift keyed (DPSK) word. 12. The system of claim 8 wherein the modulator forms the digitally modulated CW carrier using at least one waveform, and the processor includes a digital matched filter (DMF) for correlating the received propagated, digitally modulated CW carrier with the waveform. 13. A system for chemical identification of a medium comprising: a laser for generating an optical beam, a digital modulator for modulating the optical beam to form a digitally modulated optical carrier, a transmitter for transmitting the digitally modulated optical carrier through the medium, a receiver for detecting the digitally modulated optical carrier from the medium to form a detected signal, and a processor including a bit error rate (BER) measuring unit for accumulating bit error of the detected signal, and identifying the medium based on the accumulated bit error wherein the medium is characterized by a small change in SNR resulting in a relatively large change in BER. 14. The system of claim 13 wherein the laser generates a CW optical beam, the processor includes a code generator for forming an encoded word, and the digital modulator modulates the CW optical beam using the encoded word to form the digitally modulated optical carrier. 15. A method for chemically identifying a medium comprising: (a) generating a CW carrier; (b) forming an encoded word; (c) modulating the CW carrier with the encoded word to form an encoded CW carrier; (d) propagating the encoded CW carrier through a medium; (e) receiving the propagated, encoded CW carrier from the medium to form a detected signal; and (f) measuring bit error rate (BER) of the detected signal, and identifying the medium based on the measured BER, wherein the medium is characterized by a small change in SNR resulting in a relatively large change in BER. 16. The method of claim 15 wherein step (f) includes accumulating bits of the detected signal, comparing, on a bit-by-bit basis, the encoded word with the detected signal, and determining bit errors based on the comparison. 17. The method of claim 15 wherein step (b) includes forming a pseudonoise (PN) encoded word. 18. A method for chemically identifying a medium comprising: (a) generating an optical beam; (b) modulating the optical beam to form a digitally modulated optical carrier; (c) transmitting the digitally modulated optical carrier through the medium; (d) receiving the digitally modulated optical carrier from the medium to form a detected signal; and (e) measuring at least one property of the medium based on the detected signal; wherein step (e) includes measuring a bit error rate (BER), after accumulating bit errors of the detected signal, and using the accumulated bit errors to identify the medium, and wherein the medium is characterized by a small change is SNR resulting in a relatively large change in BER. 19. The method of claim 18 wherein step (a) includes generating a CW optical beam; and step (b) includes forming an encoded word for a digitally modulating the CW optical beam to form the digitally modulated optical carrier.