System and method for detecting chemical species from a remote sensing platform

1. A remote sensing system comprising:

a transmitter that transmits an online signal and first and second offline signals toward a target,

a receiver that receives a returned online signal and first and second returned offline signals from the target,

a processor configured to determine (a) a first CPL (concentration path length) value based on the returned online signal and only the first offline signal, and (b) a second CPL value based on the returned online signal and only the second offline signal, and

the processor configured to determine a first CPL mean and a first CPL standard deviation, based on a predetermined number of first CPL values,

the processor configured to determine a second CPL mean and a second CPL standard deviation, based on a predetermined number of second CPL values,

a filter that correlates the first CPL value and the second CPL value with (a) the first CPL mean and the first CPL standard deviation and (b) the second CPL mean and the second CPL standard deviation, respectively, for determining whether the first and second CPL values are useable.

2. The remote sensing system of claim 1 wherein

the processor is configured to determine the first CPL value and the second CPL value, based on a predetermined number of received returned online, first offline and second offline signals,

the processor is configured to determine a first energy value and a first energy standard deviation, based on a predetermined number of returned first offline signals;

the processor is configured to determine a second energy value and a second energy standard deviation, based on a predetermined number of returned second offline signals,

the filter is configured to determine if the following inequality is true:

IF [CPL1>(CPL1MEAN+1.5×CPL1SD) AND CPL2<CPL2MEAN AND ENERGY1>(ENERGY1+1.5×ENERGYSD1]

wherein

CPL1 is the first CPL value,

CPL2 is the second CPL value,

CPL1MEAN is the first CPL mean,

CPL2MEAN is the second CPL mean,

CPL1SD is the first CPL standard deviation,

ENERGY1 is the first energy value,

ENERGYSD1 is the first energy standard deviation,

and

the filter is subsequently configured to flag that the signals are not useable.

3. The remote sensing system of claim 1 wherein

the processor is configured to determine the first CPL value and the second CPL value, based on a predetermined number of received returned online, first offline and second offline signals,

the processor is configured to determine a first energy value and a first energy standard deviation, based on a predetermined number of returned first offline signals;

the processor is configured to determine a second energy value and a second energy standard deviation, based on a predetermined number of returned second offline signals,

the filter is configured to determine if the following inequality is true:

IF [CPL2>(CPL2MEAN+1.5×CPL2SD) AND CPL1<CPL1MEAN AND ENERGY2>(ENERGY2+1.5×ENERGYSD2)]

wherein

CPL1 is the first CPL value,

CPL2 is the second CPL value,

CPL1MEAN is the first CPL mean,

CPL2MEAN is the second CPL mean,

CPL2SD is the second CPL standard deviation,

ENERGY2 is the second energy value,

ENERGYSD2 is the second energy standard deviation

and

the filter is subsequently configured to flag that the signals are not useable.

4. The remote sensing system of claim 1 wherein

the processor is configured to determine the first CPL value and the second CPL value, based on a predetermined number of received returned online, first offline and second offline signals,

the filter is configured to determine if the following inequality is true:

IF [ABSOLUTE(CPL1−CPL2)>(ABSOLUTE(CPL1MEAN−CLPL2MEAN)+3.5×STANDARD DEVIATION OF (ABSOLUTE (CPL1−CPL2)))]

wherein

CPL1 is the first CPL value,

CPL2 is the second CPL value,

CPL1MEAN is the first CPL mean,

CPL2MEAN is the second CPL mean,

and

the filter is subsequently configured to flag that the signals are not useable.

5. The remote sensing system of claim 1 wherein

the returned online signal is set to an absorption wavelength of a species of gas,

the returned first offline signal is set to a non-absorption wavelength of the species of gas, and

the returned second offline signal is set to a non-absorption wavelength of the species of gas.

6. The remote sensing system of claim 1 wherein

the transmitted online, first offline and second offline signals form a train of pulse triplets that are repeated at a predetermined pulse repetition frequency (PRF), and

the returned online, first offline and second offline signals form another train of pulse triplets.

7. The remote sensing system of claim 5 wherein

the first offline wavelength and second offline wavelength are the same.

8. The remote sensing system of claim 6 wherein

each pulse triplet includes three pulses spaced apart at approximately 100 nanoseconds or less from each other,

each pulse triplet includes a pulse width of approximately 15-20 nanoseconds, and

each pulse triplet includes the predetermined PRF of approximately 1 KHz.

9. A remote sensing system comprising:

a differential absorption lidar (DIAL) system that transmits and receives optical signals to and from a target,

the optical signals including (a) an online signal having an absorption wavelength of a species of gas, (b) a first offline signal having a non-absorption wavelength of the species of gas, and (c) a second offline signal having a non-absorption wavelength of the species of gas,

the DIAL system determining a first concentration path length (CPL) value based on signals (a) and only (b), and determining a second CPL value based on signals (a) and only (c), and

the processor configured to determine a first CPL mean and a first CPL standard deviation, based on a predetermined number of first CPL values,

the processor configured to determine a second CPL mean and a second CPL standard deviation, based on a predetermined number of second CPL values,

a filter that correlates the first CPL value and the second CPL value with (a) the first CPL mean and the first CPL standard deviation and (b) the second CPL mean and the second CPL standard deviation, respectively, in order to assess quality of the optical signals.

10. The remote sensing system of claim 9 wherein

the filter is configured to determine if the following inequality is true:

IF [CPL1>(CPL1MEAN+1.5×CPL1SD) AND CPL2<CPL2MEAN AND ENERGY1>(ENERGY1+1.5×ENERGYSD1]

wherein

CPL1 is the first CPL value,

CPL2 is the second CPL value,

CPL1MEAN is the first CPL mean,

CPL2MEAN is the second CPL mean,

CPL1SD is the first CPL standard deviation,

ENERGY1 is the first energy value,

ENERGYSD1 is the first enemy standard deviation,

provide a flag denoting that the first CPL value is not useable.

11. The remote sensing system of claim 9 wherein

the processor is configured to determine a first energy value and a first energy standard deviation, based on a predetermined number of returned first offline signals;

the processor is configured to determine a second energy value and a second energy standard deviation, based on a predetermined number of returned second offline signals,

the filter is configured to determine if the following inequality is true:

IF [CPL2>(CPL2MEAN+1.5×CPL2SD) AND CPL1<CPL1MEAN AND ENERGY2>(ENERGY2+1.5×ENERGYSD2)]

wherein

CPL1 is the first CPL value,

CPL2 is the second CPL value,

CPL1MEAN is the first CPL mean,

CPL2MEAN is the second CPL mean,

CPL2SD is the second CPL standard deviation,

ENERGY2 is the second energy value,

ENERGYSD2 is the second energy standard deviation

provide a flag denoting that the second CPL value is not useable.

12. The remote sensing system of claim 9 wherein

the online signal includes an online pulse train having a predetermined pulse repetition frequency (PRF),

the first offline signal includes a first pulse train having the same predetermined pulse repetition frequency, and

the second offline signal includes a second pulse train having the same predetermined pulse repetition frequency.

13. The remote sensing system of claim 12 wherein

the online, first offline and second offline pulse trains are interleaved to form pulse triplets having the same predetermined pulse repetition frequency.