Abstract
Pseudo Invariant Calibration Sites (or PICS) have been in use for the past 15 years for long term trending of optical satellite radiometric stability. Those PICS in the Saharan desert have shown the best stability and have been used to show the long term stability of many satellite systems with precision of less than 3% in the visible and infrared. While the use of PICS for trending purposes has been of great value, these sites also have the potential for use in absolute calibration such that sensor performance can be assessed without requiring long periods of time. This paper reports on the development of an absolute calibration model for the well-known Libya 4 site using Hyperion data sets. Libya 4 has been identified as perhaps the most stable PICS in the Sahara Desert and, therefore, has been identified as a data collection site for the Hyperion hyperspectral sensor for the past 10 years. As a result, over 200 scenes are available for the analysis of Libya 4 providing a record that can be used to assess the atmospheric and surface properties associated with this site. Due to the hyperspectral (10 nm channel spacing) nature of the data sets, information about the surface properties can be isolated from atmospheric effects to allow development of BRDF models. Conversely, once a BRDF model has been developed, it can be used in conjunction with other wavelengths from the hyperspectral imagery to derive an atmospheric model. Using this approach, results have indicated the stability of Libya 4 at the 1% level and the ability to absolutely calibrate sensors to within the accuracies stated in the mission requirements. Details of this methodology, as well as recent updates and applications to sensors currently in orbit, will be presented.
Using Hyperion to Develop an Absolute Calibration Model for the Libya 4 Invariant Test Site - Initial Concepts
Pseudo Invariant Calibration Sites (or PICS) have been in use for the past 15 years for long term trending of optical satellite radiometric stability. Those PICS in the Saharan desert have shown the best stability and have been used to show the long term stability of many satellite systems with precision of less than 3% in the visible and infrared. While the use of PICS for trending purposes has been of great value, these sites also have the potential for use in absolute calibration such that sensor performance can be assessed without requiring long periods of time. This paper reports on the development of an absolute calibration model for the well-known Libya 4 site using Hyperion data sets. Libya 4 has been identified as perhaps the most stable PICS in the Sahara Desert and, therefore, has been identified as a data collection site for the Hyperion hyperspectral sensor for the past 10 years. As a result, over 200 scenes are available for the analysis of Libya 4 providing a record that can be used to assess the atmospheric and surface properties associated with this site. Due to the hyperspectral (10 nm channel spacing) nature of the data sets, information about the surface properties can be isolated from atmospheric effects to allow development of BRDF models. Conversely, once a BRDF model has been developed, it can be used in conjunction with other wavelengths from the hyperspectral imagery to derive an atmospheric model. Using this approach, results have indicated the stability of Libya 4 at the 1% level and the ability to absolutely calibrate sensors to within the accuracies stated in the mission requirements. Details of this methodology, as well as recent updates and applications to sensors currently in orbit, will be presented.