Fig. 4
From: Direct retrieval of isoprene from satellite-based infrared measurements
An example CrIS isoprene retrieval over Amazonia (8.698°S, 69.134°W) on September 30, 2014. a Calculated (blue) spectrum overlaid on the CrIS-measured (black) spectrum, plotted in brightness temperature units. The major features are due to H2O vapor. b Residual spectra (observed—calculated) after accounting for water vapor (H2O), nitric acid (HNO3), ammonia (NH3), and relevant surface and cloud properties. The purple line indicates the residual spectrum before accounting for isoprene (C5H8), clearly showing the isoprene signals peaking at 893.75 cm−1 (ν28 band) and 906.25 cm−1 (ν27 band). The green line depicts the residuals after fitting for isoprene. The red dashed lines denote the single-pixel CrIS noise level as reported in the CrIS L1B data product. c Difference between the residual spectra when including vs. excluding atmospheric isoprene in the fitting—illustrating the isoprene spectral signal in this example. d A priori (blue) and retrieved (green) isoprene volume mixing ratios (VMR). e Sum of the rows of the averaging kernel matrix for the isoprene retrieval, showing 0.9 degrees of freedom for signal (DOFS) in this example. f Estimated uncertainty of the retrieval
