On-orbit aqua MODIS modulation transfer function trending in along-scan from the Spectro-Radiometric Calibration Assembly

Taeyoung Choi; Nianzeng Che; Xiaoxiong Xiong

doi:10.1117/12.793844

20 August 2008 On-orbit aqua MODIS modulation transfer function trending in along-scan from the Spectro-Radiometric Calibration Assembly

Taeyoung Choi, Nianzeng Che, Xiaoxiong Xiong

Author Affiliations +

Proceedings Volume 7081, Earth Observing Systems XIII; 70810A (2008) https://doi.org/10.1117/12.793844
Event: Optical Engineering + Applications, 2008, San Diego, California, United States

Abstract

The Spectro-Radiometric Calibration Assembly (SRCA) is one of the on-board calibrators for the MODIS instrument. The SRCA is operated in three modes: spectral, spatial, and radiometric. The spatial mode is used to track the changes in band-to-band registration both along-scan (band and detector) and along-track (band) and the MTF in the along-scan direction for all 36 MODIS bands over the MODIS lifetime. In the SRCA spatial mode, a rectangular knife-edge reticle, located at the focus of the SRCA collimator, is imaged onto four MODIS Focal Plane Assemblies (FPA). The reticle is illuminated by a spherical integration sphere and a glow-bar so that all bands can have an appropriate signal level. When the MODIS scan mirror rotates, the illuminated knife-edge scans across the bands/detectors. In addition, there are five electronic phase-delays so that the sampling spacing is reduced to 1/5 of the detector size, which results in dense data points. After combining detector responses from all phase-delays, a combined bell-shaped response profile is formed. The derivative of the detector response to the knife-edge is the Line Spread Function (LSF). In the frequency domain, the Modulation Transfer Functions (MTF) are calculated from the normalized Fourier transform of the LSF. The MTF results from the SRCA are validated by the pre-launch results from the Integrated Alignment Collimator (IAC) and a SRCA collection performed in the Thermal Vacuum (TV). The six-year plus on-orbit MTF trending results show very stable responses in the VIS and NIR FPAs, and meet the design specifications. Although there are noticeable MTF degradations over the instrument lifetime in bands 1 and 2, they are negligible with the large specification margins. In addition, a similar relationship is found between the band locations in the VIS and NIR FPAs versus MTF values.

Citation Download Citation

Taeyoung Choi, Nianzeng Che, and Xiaoxiong Xiong "On-orbit aqua MODIS modulation transfer function trending in along-scan from the Spectro-Radiometric Calibration Assembly", Proc. SPIE 7081, Earth Observing Systems XIII, 70810A (20 August 2008); https://doi.org/10.1117/12.793844

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available