Cross Calibration of the OceanSAT -2 Scatterometer With QuikSCAT Scatterometer Using Natural Terrestrial Targets

Abstract

The accuracy of ocean surface wind vectors measured by satellite-borne scatterometers depends on measured backscattering coefficient (σ • ). Hence, an in-flight calibration of a satellite scatterometer is essential as this is not guaranteed by its prelaunch absolute calibration. The postlaunch calibration of σ • is also required to monitor the time evolution of the accuracy of measured σ • . This is performed using relative calibration over land targets with minor spatiotemporal variation of σ • . A few such targets are the Amazon rainforest, Greenland, Antarctica, etc. In this paper, relative calibration of σ • from the OceanSAT-2 Scatterometer (OSCAT) has been carried out by comparing it with a similar quantity from the Quick Scatterometer (QuikSCAT) for November 2009. The differences between the average σ • of QuikSCAT and that of OSCAT have been calculated globally to check the overall consistency. Over the calibration sites, the differences are within ±0.25 dB. Histograms of differences in ascending/descending passes and fore/aft looks of OSCAT have also been analyzed over the calibration sites. These indicate that look bias in OSCAT σ • is within the range of ±0.5 dB. It is also evident that pass biases, i.e., differences between ascending and descending passes, exist over the Amazon rainforest for both QuikSCAT and OSCAT. This diurnal variation in σ • may go up to 1.25 dB in OSCAT. Further, computations of daily average and standard deviation over the calibration site show that mean OSCAT σ • is consistent with mean QuikSCAT σ • , whereas the standard deviation in OSCAT is marginally higher. Further, time-series analysis of OSCAT σ • shows its temporal stability.

Evaluating and Extending the Ocean Wind Climate Data Record

“…The brief OSCAT-1 and spinning QuikSCAT overlap period in November 2009 was used by [59] for cross calibration, but a longer-term Ku-band radar reference is desirable to span the lifetimes of multiple sensors. Beginning in late 1997 with the launch of TRMM, continuous Ku-band surface backscatter observations have been collected by the NASA/JAXA Precipitation Radar (PR) (science operations ended in late 2014), and the GPM dualfrequency precipitation radar (DPR) (March 2014-current), giving an approximate 9-month overlap period.…”

A Perspective on the Performance of the CFOSAT Rotating Fan-Beam Scatterometer

“…It provided high-quality wind data for more than 10 years until the failure of its spinning antenna in November 2009. A similar version of this instrument has been launched by various countries, such as the NASA SeaWinds-2 onboard the Japanese ADEOS-2 satellite (December 2002-October 2003, OSCAT onboard the Indian Oceansat-2 satellite (September 2009-February 2014) [9], HSCAT on the Chinese HY-2A satellite (since August 2011) [10], the NASA RapidScat installed on the International Space Station (September 2014-August 2016) [11], and the Indian scatterometer satellite (SCATSAT-1, since September 2016) [12].…”

Comparison of sea ice classification methods based on satellite scatterometer and radiometer data in the Weddell Sea, Antarctica

“…It has a pencil-beam antenna and, similarly to QuikSCAT, it operates at the Ku-Band with a frequency of 13.5 GHz (wavelength 2.22 cm). OSCAT, operating from November 2009–February 2014, has an HH inner beam covering a swath width of 1400 km at an incidence angle of 49° and a VV outer beam covering a swath width of 1800 km at an incidence angle of 57° (Bhowmick et al 2014).…”