Vincent V. Salomonson

MODIS Snow-Cover Products

Abstract On December 18, 1999, the Terra satellite was launched with a complement of five instruments including the Moderate Resolution Imaging Spectroradiometer (MODIS). Many geophysical products are derived from MODIS data including global snow-cover products. MODIS snow and ice products have been available through the National Snow and Ice Data Center (NSIDC) Distributed Active Archive Center (DAAC) since September 13, 2000. MODIS snow-cover products represent potential improvement to or enhancement of the currently available operational products mainly because the MODIS products are global and 500-m resolution, and have the capability to separate most snow and clouds. The MODIS snow-mapping algorithms are automated, which means that a consistent data set may be generated for long-term climate studies that require snow-cover information. Extensive quality assurance (QA) information is stored with the products. The MODIS snow product suite begins with a 500-m resolution, 2330-km swath snow-cover map, which is then gridded to an integerized sinusoidal grid to produce daily and 8-day composite tile products. The sequence proceeds to a climate-modeling grid (CMG) product at 0.05° resolution, with both daily and 8-day composite products. Each pixel of the daily CMG contains fraction of snow cover from 40% to 100%. Measured errors of commission in the CMG are low, for example, on the continent of Australia in the spring, they vary from 0.02% to 0.10%. Near-term enhancements include daily snow albedo and fractional snow cover. A case study from March 6, 2000, involving MODIS data and field and aircraft measurements, is presented to show some early validation work.

Development of methods for mapping global snow cover using moderate resolution imaging spectroradiometer data

Abstract An algorithm is being developed to map global snow cover using Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) data beginning at launch in 1998. As currently planned, digital maps will be produced that will provide daily, and perhaps maximum weekly, global snow cover at 500-m spatial resolution. Statistics will be generated on the extent and persistence of snow cover in each pixel for each weekly map, cloud cover permitting. It will also be possible to generate snow-cover maps at 250-m spatial resolution using MODIS data, and to study snow-cover characteristics. Preliminary validation activities of the prototype version of our snow-mapping algorithm, SNOMAP, have been undertaken. SNOMAP will use criteria tests and a decision rule to identify snow in each 500-m MODIS pixel. Use of SNOMAP on a previously mapped Landsat Thematic Mapper (TM) scene of the Sierra Nevadas has shown that SNOMAP is 98 % accurate in identifying snow in pixels that are snow covered by 60% or more. Results of a comparison of a SNOMAP classification with a supervised-classification technique on six other TM scenes show that SNOMAP and supervised-classification techniques agree to within about 11 % or less for nearly cloud-free scenes and that SNOMAP provided more consistent results. About 10 % of the snow cover, known to be present on the 14 March 1991 TM scene covering Glacier National Park in northern Montana, is obscured by dense forest cover. Mapping snow cover in areas of dense forests is a limitation in the use of this procedure for global snow-cover mapping. This limitation, and sources of error will be assessed globally as SNOMAP is refined and tested before and following the launch of MODIS.

Terrestrial remote sensing science and algorithms planned for EOS/MODIS

Abstract The Moderate Resolution Imaging Spectroradiometer (MODIS) will be the primary daily global monitoring sensor on the NASA Earth Observing System (EOS) satellites, scheduled for launch on the EOS-AM platform in June 1998 and the EOS-PM platform in December 2000. MODIS is a 36 channel radiometer covering 0·415-14·235 μm wavelengths, with spatial resolution from 250 m to 1 km at nadir. MODIS will be the primary EOS sensor for providing data on terrestrial biospheric dynamics and process activity. This paper presents the suite of global land products currently planned for EOSDIS implementation, to be developed by the authors of this paper, the MODIS land team (MODLAND). These include spectral albedo, land cover, spectral vegetation indices, snow and ice cover, surface temperature and fire, and a number of biophysical variables that will allow computation of global carbon cycles, hydrologic balances and biogeochemistry of critical greenhouse gases. Additionally, the regular global coverage of these var...

Large seasonal swings in leaf area of Amazon rainforests

Despite early speculation to the contrary, all tropical forests studied to date display seasonal variations in the presence of new leaves, flowers, and fruits. Past studies were focused on the timing of phenological events and their cues but not on the accompanying changes in leaf area that regulate vegetation–atmosphere exchanges of energy, momentum, and mass. Here we report, from analysis of 5 years of recent satellite data, seasonal swings in green leaf area of ≈25% in a majority of the Amazon rainforests. This seasonal cycle is timed to the seasonality of solar radiation in a manner that is suggestive of anticipatory and opportunistic patterns of net leaf flushing during the early to mid part of the light-rich dry season and net leaf abscission during the cloudy wet season. These seasonal swings in leaf area may be critical to initiation of the transition from dry to wet season, seasonal carbon balance between photosynthetic gains and respiratory losses, and litterfall nutrient cycling in moist tropical forests.

Multiyear On-Orbit Calibration and Performance of Terra MODIS Reflective Solar Bands

Terra Moderate Resolution Imaging Spectroradiometer (MODIS) has made continuous global observations for more than six years since its launch in December 1999. MODIS has 36 spectral bands: 20 reflective solar bands (RSBs) with wavelengths from 0.41-2.2 mum and 16 thermal emissive bands with wavelengths from 3.7-14.4 mum. It is a cross-track scanning radiometer that collects data at three nadir spatial resolutions: 0.25 km (2 bands), 0.5 km (5 bands), and 1 km (29 bands). An onboard solar diffuser (SD) and an SD stability monitor (SDSM) are used biweekly for RSB on-orbit radiometric calibration. Another onboard calibrator (OBC), a spectroradiometric calibration assembly, is used periodically to evaluate and monitor RSB spatial and spectral performance. In addition to measurements made using OBCs, lunar observations at nearly identical phase angles are used to track RSB calibration stability. This paper provides an overview of MODIS RSB on-orbit calibration algorithms and operational activities. It discusses sensor characteristics that could impact RSB calibration accuracy and data product quality, including degradation of the SD bidirectional reflectance factor (BRF), degradation of the scan mirror reflectance in the visible spectral region, and changes in operational configuration. The Terra MODIS OBCs have performed well in monitoring SD degradation and tracking changes in RSB response. Band 8 (0.41 mum) has experienced the largest response decrease with an approximate annual rate of 4.5% (mirror side 1). Band 9 (0.44 mum) has an annual response decrease of about 2.3% (mirror side 1). For most RSB bands with wavelengths greater than 0.5 mum, the annual response changes are generally less than 1.0%. Results from the SDSM on-orbit observations show that the SD BRF also has a similar wavelength-dependent degradation, with the largest degradation appearing at the shortest wavelengths. Among the 330 RSB detectors, there are no inoperable detectors, and only a few noisy detectors have appeared postlaunch

Development of the Aqua MODIS NDSI fractional snow cover algorithm and validation results

The principal purpose of this paper is to describe the development and validation of an algorithm to estimate the fraction of snow cover within a 500-m pixel of the Moderate Resolution Imaging Spectroradiometer (MODIS) operating on the Earth Observing System Aqua spacecraft. The performance of this algorithm and algorithms applicable to the MODIS on the Terra spacecraft are compared. Validation efforts show that both pixel-level, fractional snow cover relationships for the Terra and Aqua MODIS instruments work well as quantified by such measures as correlation coefficient (r) and root-mean-square error when compared to Landat-7 Enhanced Thematic Mapper ground-truth observations covering a substantial range of snow cover conditions. Over all the scenes used herein, the correlation coefficients were near 0.9 and the RMSE near 0.10. However, somewhat better performance was found for the Terra MODIS versus the Aqua MODIS over nearly concurrently observed scenes. Furthermore, it is clear that more improvements in fractional snow cover estimates within MODIS pixels should be pursued to better account for variability in slope and aspect, atmospheric effects, snow cover types, and land cover

On-orbit performance of the Earth Observing System Moderate Resolution Imaging Spectroradiometer; first year of data

Abstract The Moderate Resolution Imaging Spectroradiometer (MODIS) completed the first year of science data acquisition on February 24, 2000. The overall performance of the sensor and the on-board calibration systems for this first year have been very good. Several features of the performance lead to characteristics in the data set that merit special attention. These items are sometimes called data product caveats, and are described here. Uncertainty budgets for the 0.555-μm band, the 1.240-μm band and the 12.000-μm band are presented at several days throughout this first year. The uncertainty is estimated to be decreasing with time during this period, and to be near 1.8% in reflectance factor for 0.555 μm, 1.9% for the reflectance factor product for the 1.240 μm band, and 0.7% for the 12.000-μm band at nadir at the end of the first year. Degradation of the solar diffuser is 2.3% at 0.412 μm, known to an uncertainty of ±0.5%. Solar diffuser degradation for wavelengths longer that 0.5 μm is indistinguishable from the uncertainty in trend determination for the first year. Mirror side degradation at 0.412 μm is 6±0.5%, with a mirror side difference of an additional 3%. The performance present in the data at the end of year 1 provides significant encouragement that many improvements in our understanding of the Earth system performance can and will be based on MODIS data during the coming years.

On-Orbit Calibration and Performance of Aqua MODIS Reflective Solar Bands

Aqua MODIS has successfully operated on-orbit for more than six years since its launch in May 2002, continuously making global observations and improving studies of changes in the Earths climate and environment. Twenty of the 36 MODIS spectral bands, covering wavelengths from 0.41 to 2.2 ?m, are the reflective solar bands (RSBs). They are calibrated on-orbit using an onboard solar diffuser (SD) and an SD stability monitor. In addition, regularly scheduled lunar observations are made to track the RSB calibration stability. This paper presents Aqua MODIS RSB on-orbit calibration and characterization activities, methodologies, and performance. Included in this paper are characterizations of detector signal-to-noise ratio, short-term stability, and long-term response change. Spectral-wavelength-dependent degradation of the SD bidirectional reflectance factor and scan mirror reflectance, which also varies with the angle of incidence, is examined. On-orbit results show that Aqua MODIS onboard calibrators have performed well, enabling accurate calibration coefficients to be derived and updated for the Level 1B production and assuring high-quality science data products to be continuously generated and distributed. Since launch, the short-term response, on a scan-by-scan basis, has remained extremely stable for most RSB detectors. With the exception of band 6, there have been no new RSB noisy or inoperable detectors. Like its predecessor, i.e., Terra MODIS, launched in December 1999, the Aqua MODIS visible spectral bands have experienced relatively large changes, with an annual response decrease (mirror side 1) of 3.6% for band 8 at 0.412 ?m, 2.3% for band 9 at 0.443 ?m, 1.6% for band 3 at 0.469 ?m, and 1.2% for band 10 at 0.488 ?m. For other RSB bands with wavelengths greater than 0.5 ?m, the annual response changes are typically less than 0.5%. In general, Aqua MODIS optics degradation is smaller than Terra MODIS, and the mirror-side differences are much smaller. Overall, Aqua MODIS RSB on-orbit performance is better than that of Terra MODIS.

An overview of the Earth Observing System MODIS instrument and associated data systems performance

The MODIS instrument on the EOS Terra Mission has completed over 2 years of successful operation. Excellent data products have been developed and a full year or more of these products are now available. Validation of these products is continuing and efforts to improve product availability and access are underway. The MODIS on the EOS Aqua satellite is projected to become operational in 2002.

MODIS: a global imaging spectroradiometer for the Earth Observing System

MODIS, a 36 band (0.42 - 14.24 micrometer) moderate resolution imaging spectroradiometer is the keystone sensor for the 15 year (1998-2013) Earth Observing System (EOS). MODIS sensors on both the AM and PM EOS spacecraft will each collect data from the entire globe every two days. This data will be used to generate numerous scientific products which will enhance knowledge of changes in the global climate system due to both natural and anthropogenic causes. MODIS, under development by the Santa Barbara Research Center (SBRC), Goleta, California, and the EOS Project at the Goddard Space Flight Center (GSFC), Greenbelt, Maryland, will include bands with spatial resolutions of 250, 500 or 1,000 meters at nadir, SNR’s as large as several thousand, onboard spatial, spectral and radiometric calibration, solar and lunar radiometric stability monitoring, knowledge of pixel location to less than 500 meters (including spacecraft errors) and radiometric accuracy of 5 percent or less for the 19 reflected solar bands and 1 percent or less for the 17 thermal emission bands. Polarization sensitivity will be limited to less than two percent for bands with wavelengths less than 2.2 micrometers.