Albert J. Fleig

Achieving sub-pixel geolocation accuracy in support of MODIS land science

The Moderate Resolution Imaging Spectroradiometer (MODIS) was launched in December 1999 on the polar orbiting Terra spacecraft and since February 2000 has been acquiring daily global data in 36 spectral bands—29 with 1 km, five with 500 m, and two with 250 m nadir pixel dimensions. The Terra satellite has on-board exterior orientation (position and attitude) measurement systems designed to enable geolocation of MODIS data to approximately 150 m (1r) at nadir. A global network of ground control points is being used to determine biases and trends in the sensor orientation. Biases have been removed by updating models of the spacecraft and instrument orientation in the MODIS geolocation software several times since launch and have improved the MODIS geolocation to approximately 50 m (1r) at nadir. This paper overviews the geolocation approach, summarizes the first year of geolocation analysis, and overviews future work. The approach allows an operational characterization of the MODIS geolocation errors and enables individual MODIS observations to be geolocated to the sub-pixel accuracies required for terrestrial global change applications. D 2002 Elsevier Science Inc. All rights reserved.

Total Ozone Determination from the Backscattered Ultraviolet (BUV) Experiment

Abstract The algorithm used to derive total ozone from the Nimbus 4 Backscattered Ultraviolet (BUV) experiment is described. A seven-year global data set with more than one million retrievals has been produced and archived using this algorithm. The algorithm is a physical retrieval scheme using accurate radiative transfer computations. Error sources are discussed and verified using Dobson network comparisons and the statistics of the BUV A- and B-pair derived ozone values.

Key characteristics of MODIS data products

Forty science products totaling 600 GB of storage volume per day will be produced from NASAs Moderate Resolution Imaging Spectroradiometer (MODIS). Eighty-five percent of this data volume is in products that are in the instruments scan geometry (processing Levels 1 and 2) that are not Earth located. Before ordering MODIS data products, users should consider processing level, data formats, product size, and the unique characteristics of MODIS products. Given the data volumes associated with the MODIS Levels 1 and 2 products, the resources required to process them and the issues associated with the scanning geometry of the instrument, users are encouraged to order data products that are Earth located. These include Level 3 products, which are produced on fixed global grids and Level 2G products, in which observations and their Earth location have been stored in bins of the MODIS global grids.

Standard Ozone Profiles from Balloon and Satellite Data Sets

Abstract Standard profiles based on upper level averaged profiles From BUV and lower level averaged profiles from balloon measurements are presented in a parametric representation as a function of time of year and latitude. The representation is a simple 4-parameter function representing the ozone amount (m-atm-cm) in each of 12 atmospheric layers defined following the standard Umkehr convention. The same parameterization is applied to the Nimbus-7 SBUV data and is compared to the BUV/balloon parameterization. The ozone variance unaccounted for by the representation is presented and discussed. The season-latitude representation reduces considerably the ozone variance at all levels and explains much of the correlation between layers. This simple representation and corresponding covariance matrix have been used as a priori information in the ozone vertical profile inversion of the Nimbus-7 SBUV experimental measurements.

Standard profiles of ozone from ground to 60 km obtained by combining satellite and ground based measurements

Recent satellite experiments have produced a large multi-year data base of stratospheric ozone profiles covering the entire globe. Among these, the Solar Backscatter Ultraviolet Experiment (SBUV) has been operating continuously since November 1978 providing some 1000 profiles per day. Based on detailed comparisons with ozonesondes and other satellite based instruments, SBUV data have been determined to be of excellent quality from about 50 km down to the tropopause.

MODIS geolocation algorithm and error analysis tools

The Moderate Resolution Imaging Spectroradiometer (MODIS) contains 36 bands from the visible to the thermal infrared with the nominal ground field of views of 250 m, 500 m and 1 km. This paper summarizes the MODIS Earth location algorithm from the focal plane/detector system through the telescope system, rotating scan mirror system, spacecraft ephemeris/attitude processing system, and digital elevation model. It also describes how the geolocation of other bands can be derived from the ideal band ground coordinates. Some tools have been developed to check the model accuracy and validity of the geolocation. This paper describes these tools including a ground control point matching program, a trend and bias error analysis program, and a MODIS image simulation program using Landsat TM (Thematic Mapper) images. Some post launch findings on the model accuracy and necessary changes to the model are also described.

The MODIS operational geolocation error analysis and reduction methodology

The operational methodology used to analyze and reduce errors caused by biases and trends in the Moderate Resolution Imaging Spectroradiometer (MODIS) geolocation data is described. MODIS is scheduled for launch in 1999 on the polar orbiting EOS-AM1 satellite and will acquire daily global data in 36 spectral bands at three spatial resolutions. The satellite has onboard exterior orientation measurement systems designed to enable unaided geolocation of MODIS data to approximately 450 m (3/spl sigma/). A global network of ground control points will be used to improve the navigation to approximately 150 m (3/spl sigma/). The ground control points will be used to determine static biases in the interior orientation every MODIS repeat cycle (16 days). Over longer periods analyses will be performed to determine if there are any trends or cyclical variations. This approach will allow an operational characterization of the MODIS geolocation errors and will enable individual observations to be geolocated to the sub-pixel accuracies required for terrestrial global change applications.

The MODIS operational geolocation error analysis and reduction early results

The Moderate Resolution Imaging Spectroradiometer (MODIS) was launched December 1999 on the polar orbiting Terra satellite and since February 2000 has been acquiring earth observation data. The Terra satellite has onboard exterior orientation (position and attitude) measurement systems designed to enable unaided navigation of MODIS data to within approximately 150 m (1/spl sigma/) at nadir. A global network of ground control points will be used to improve the navigation to approximately 50 m (1/spl sigma/). This approach allows an operational characterization of the MODIS geolocation errors and enables individual MODIS observations to be geolocated to the sub-pixel accuracies required for terrestrial global change applications.

Resources for developing algorithms and processing Level 1A and geolocation information

Every satellite data system starts with some form of Level 1 and geolocation processing. This paper provides information to help future missions better estimate the personnel, schedule, and computing requirements for their data processing and algorithm development. The level of development effort and the computational resources for Level 1A and geolocation processing for the MODIS instrument are described. This information is related to the requirements for the Level 1A and geolocation tasks. Estimates of how both development and processing resource requirements scale to these functional requirements are provided.

Release 2 data products from the Ozone Mapping and Profiler Suite (OMPS) Limb Profiler

The OMPS Limb Profiler (LP) was launched on board the NASA Suomi National Polar-orbiting Partnership (SNPP) satellite in October 2011. OMPS-LP is a limb-scattering hyperspectral sensor that provides ozone profiling capability at 1.8 km vertical resolution from cloud top to 60 km altitude. The use of three parallel slits allows global coverage in approximately four days. We have recently completed a full reprocessing of all LP data products, designated as Release 2, that improves the accuracy and quality of these products. Level 1 gridded radiance (L1G) changes include intra-orbit and seasonal correction of variations in wavelength registration, revised static and intra-orbit tangent height adjustments, and simplified pixel selection from multiple images. Ozone profile retrieval changes include removal of the explicit aerosol correction, exclusion of channels contaminated by stratospheric OH emission, a revised instrument noise characterization, improved synthetic solar spectrum, improved pressure and temperature ancillary data, and a revised ozone climatology. Release 2 data products also include aerosol extinction coefficient profiles derived with the prelaunch retrieval algorithm. Our evaluation of OMPS LP Release 2 data quality is good. Zonal average ozone profile comparisons with Aura MLS data typically show good agreement, within 5-10% over the altitude range 20-50 km between 60°S and 60°N. The aerosol profiles agree well with concurrent satellite measurements such as CALIPSO and OSIRIS, and clearly detect exceptional events such as volcanic eruptions and the Chelyabinsk bolide in February 2013.