# A Geostationary Instrument Simulator for Aerosol Observing System Simulation Experiments
## 4 Concluding Remarks and Outlook  
In this paper we described a detailed and accurate (less than 1.0% uncertainty) model for calculating TOA radiance from the GEOS-5 nature run for a constellation of geostationary sensors for observing air quality. The current generation of aerosol retrieval algorithms are optimized for specific conditions such as afternoon well-mixed atmospheres, and limited viewing and illumination angles. The G5 NR and the simulated observations described in this document provide an opportunity to test these algorithms globally over a realistic dynamic range. A combined TEMPO and GOES-R retrieval algorithm for aerosol type detection based on empirical thresholds of aerosol index derived from MODIS observations was demonstrated and evaluated using the simulated observations. We found that the combination of UV-Vis observations from TEMPO and near-infrared observations from GOES-R can be used to accurately detect dense smoke. However, to achieve greater accuracy in aerosol detection, re-training the algorithm thresholds for the combined GOES-R and TEMPO viewing geometries is recommended as neglecting the difference in surface bidirectional reflectance between the different viewing angles can lead to missed detections. To improve dust detection, deriving aerosol index thresholds for different land surface types is recommended. This analysis coincidentally showed that the optical properties of the smoke aerosols in the simulated observations are consistent with the MODIS observations from which the aerosol index thresholds were derived. There are many more potential applications for the simulated observations described in this paper, such as establishing new retrievals or instrument requirements during the development of new mission concepts. For example, the data will be used to prototype retrievals using polarized multi-angle and multi-channel observations spanning the UV and visible wavelengths, which have the potential to provide several pieces of information beyond AOD such as aerosol absorption and fine mode fraction. The synthetic observations will also be used to analyze how the new time resolved  
Figure 18: (**a**) Ratio of simulated 412 nm to 440 nm surface reflectance, and (**b**) simulated 440 nm surface reflectance for 13 May 2007 at 20 UTC. The black and purple contours represent the areas that were detected as smoke by the VIIRS aerosol detection algorithm. measurements and the increase in spatial coverage from geostationary orbit effects chemical weather forecasts and data analysis, particularly with respect to the current suite of LEO observations. Future development of the instrument simulator capabilities will focus on including molecular absorption effects from water vapor and trace gases in the radiance calculation. This will be required for applications that use the hyperspectral feature of the new instruments. This will also require trace gas vertical profile inputs from a full chemistry nature run [63]. Furthermore, we are currently developing instrument simulator capabilities for ocean color instruments, such as PACE (Plankton, Aerosol, Cloud, ocean Ecosystem), that include detailed hyperspectral water leaving radiance calculations. These developments will provide the opportunity to test strategies for handling complex trace gas, aerosol, cloud, and surface interactions in retrieval algorithms [11; 64; 65]. Conceptualization, P.C. ([PERSON]), A.M.d.S., A.S.D. and S.K. ; Data curation, P.C. ([PERSON]), A.S.D., V.B., R.C.G. and P.C. ([PERSON]); Formal analysis, P.C. ([PERSON]), A.S.D., V.B. and P.C. ([PERSON]); Funding acquisition, A.M.d.S. and S.K. ; Investigation, P.C. ([PERSON]) and P.C. ([PERSON]); Methodology, P.C. ([PERSON]), A.M.d.S. and A.S.D. ; Project administration, A.M.d.S. ; Resources, A.M.d.S. and S.K. ; Software, P.C. ([PERSON]); Supervision, A.M.d.S. and S.K. ; Validation, P.C. ([PERSON]), A.S.D. and V.B. ; Visualization, P.C. ([PERSON]), A.S.D. and V.B. ; Writing--original draft, P.C. ([PERSON]), A.S.D. and P.C. ([PERSON]); Writing--review & editing, P.C.