Active remote sensing using a simultaneous spectral sampling technique

A method of remotely sensing a sample, comprising:

• transmitting a beam of optical radiation toward the sample, the beam including an amplitude modulated component at a first frequency and another amplitude modulated component at a second frequency, wherein the first frequency is not harmonically related to and is different from the second frequency;
• detecting the beam of optical radiation after scattering/reflecting from the sample to produce a remote detection signal;
• determining a portion of the remote detection signal that is present at the first frequency;
• determining another portion of the remote detection signal that is present at the second frequency;
• and
• obtaining information about the sample based on the portion of the remote detection signal and the portion of the remote detection signal.

A system for sensing a characteristic of a sample, comprising:

• a tunable wavelength source configured to emit first optical radiation that varies over a wavelength range at a sweep frequency;
• a reference source configured to emit second optical radiation at a fixed reference wavelength;
• a first modulator configured to modulate the first optical radiation at a first frequency;
• a second modulator configured to modulate the second optical radiation at a second frequency that is different from the first frequency and the sweep frequency, and is not harmonically related to the first frequency;
• a science detector configured to detect the optical radiation from the first modulator and the second modulator after scattering/reflecting from the sample and generate a science signal;
• a plurality of lock-in amplifiers respectively configured to generate components of the science signal that are present at the first and second frequencies;
• and
• a processor configured to determine a characteristic of the sample based on the components of the science signal that are present at the first and second frequencies.

A method of determining a concentration of material in a sample, comprising:

• modulating wavelength-varying radiation at a first frequency;
• modulating fixed-wavelength radiation at a second frequency;
• detecting the wavelength-varying radiation and the fixed-wavelength radiation before scattering/reflecting from the sample to produce a local detection signal;
• transmitting the wavelength-varying radiation and the fixed-wavelength radiation to the sample;
• detecting the wavelength-varying radiation and the fixed-wavelength radiation after scattering/reflecting from the sample to produce a remote detection signal;
• determining portions of the local detection signal and the remote detection signal at the first frequency;
• determining portions of the local detection signal and the remote detection signal at the second frequency;
• obtaining a transmission profile from the portions of the local detection signal and the remote detection signal at the first frequency and at the second frequency;
• and
• calculating the concentration of the material based on the transmission profile,
• wherein the first frequency is not harmonically related to and is different from the second frequency.

A system for remotely sensing a sample, comprising:

• means for generating wavelength-varying radiation and fixed-wavelength radiation;
• means for modulating the wavelength-varying radiation at a first frequency;
• means for modulating the fixed-wavelength radiation at a second frequency;
• and
• means for detecting radiation at the first and second frequencies using a phase sensitive technique after the wavelength-varying radiation and the fixed-wavelength radiation have scattered/reflected from the sample,
• wherein the first frequency is not harmonically related to and is different from the second frequency.