A Wider Field-of-View is Better: Quantifying the Information on Trends in Cloud-Fraction from Narrow- and Wide Field-of-View Instruments Using ARM data

Passive remote sensing of cloud fields provides wide field-of-view (WFOV) data on the spatial extent and, to varying degrees, the optical properties of clouds, while narrow field-of-view (NFOV) instruments, such as radars and lidars, can potentially provide much more information about the vertical structure and micro- and macro-physical properties of clouds. In general, we expect that wide field-of-view instruments contain more information about cloud fraction, but what is the extra information contained within WFOV instruments regarding continuous observations of cloud fraction as compared to NOV instruments? What are the implications for long-term trends in cloud properties?

We show that under a frozen-turbulence limit, we expect between 2.5 and 5 times as much information on cloud fraction from a WFOV instrument as compared to a NFOV instrument. Alternatively, we show that we can expect between 6 and 25 times as much information with the evolve-in-place limit.

Using long-duration observations of cloud-fraction from the U.S. Department of Energy's Atmospheric Radiation Measurement Program's Southern Great Plains (ARM SGP) Central Facility from the Total Sky Imager, we quantify this additional information in WFOV vs NFOV instruments. We do this by observing the time required to produce statistically indistinguishable probability distribution functions of cloud fraction between WFOV cloud-fraction and NFOV cloud fraction. We evaluate the seasonal variability in this convergence and whether there are differences within season for convergence over the 20-year TSI record. Finally, we discuss the implications for developing long-duration observationally-based trends in cloud products such as cloud fraction from remote-sensing.