1：Experimental Design and Method Selection:

The study employs an all fibered NIR-LHR in ground-based solar occultation mode, using a 1 × 2 fiber optical switch as an alternative modulator to traditional chopper for stability and compactness. Two DFB lasers at 1.6 μm and 1.65 μm serve as local oscillators for probing CO2 and CH4 absorption lines, respectively.

2：6 μm and 65 μm serve as local oscillators for probing CO2 and CH4 absorption lines, respectively. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Solar radiation containing atmospheric absorption information is captured by a custom-made solar tracker. Measurements were performed over six months in Hefei, China.

3：List of Experimental Equipment and Materials:

Includes a fiber collimator, fiber optical switch, DFB lasers, fiber couplers, high-speed photo-detectors, RF processing modules, band-pass filters, Schottky diode, lock-in amplifier, and a PC with DAQ card for data acquisition and control.

4：Experimental Procedures and Operational Workflow:

Solar radiation is chopped at 250 Hz, coupled with local oscillators, and detected by high-speed photo-detectors. The beat signals are processed to extract DC and AC components for monitoring and RF processing. Data acquisition and instrumental control are managed via LabVIEW software.

5：Data Analysis Methods:

Data retrievals were performed using the optimal estimation method (OEM) based on a radiative transfer forward model. A correlation correction method was used for wavenumber calibration, and a wavelet de-noising method was applied in data processing.