Xiaozhen Xiong

Snow grain size retrieved from near‐infrared radiances at multiple wavelengths

A comprehensive forward radiative transfer model is used to construct a snow grain size retrieval algorithm that relies on the use of NIR radiances. Data collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) at the wavelengths 0.86, 1.05, 1.24 and 1.73 µm are used to retrieve snow grain size. Based on a single-layer (homogeneous) snow model, the retrieved snow grain size appears to depend on wavelength. The photon penetration depth defined as the e-folding flux attenuation depth has be computed for different snow grain sizes and different wavelengths. It reveals that this apparent wavelength dependence occurs because (i) the snow grain size generally increases with depth, and (ii) the photon penetration depth decreases with increasing wavelength. The results show that the wavelength dependence of the photon penetration depth can be used to retrieve the depth dependence of the snow grain size.

Surface Albedo over the Arctic Ocean Derived from AVHRR and Its Validation with SHEBA Data

A method is presented for retrieving the broadband albedo over the Arctic Ocean using advanced very high resolution radiometer (AVHRR) data obtained from NOAA polar-orbiting satellites. Visible and near-infrared albedos over snow and ice surfaces are retrieved from AVHRR channels 1 and 2, respectively, and the broadband shortwave albedo is derived through narrow-to-broadband conversion (NTBC). It is found that field measurements taken under different conditions yield different NTBC coefficients. Model simulations over snow and ice surfaces based on rigorous radiative transfer theory support this finding. The lack of a universal set of NTBC coefficients implies a 5%‐10% error in the retrieved broadband albedo. An empirical formula is derived for converting albedo values from AVHRR channels 1 and 2 into a broadband albedo under different snow and ice surface conditions. Uncertain calibration of AVHRR channels 1 and 2 is the largest source of uncertainty, and an error of 5% in satellite-measured radiance leads to an error of 5%‐10% in the retrieved albedo. NOAA-14 AVHRR data obtained over the Surface Heat Budget of the Arctic Ocean (SHEBA) ice camp are used to derive the seasonal variation of the surface albedo over the Arctic Ocean between April and August of 1998. Comparison with surface measurements of albedo by Perovich and others near the SHEBA ice camp shows very good agreement. On average, the retrieval error of albedo from AVHRR is 5%‐10%.

The CrIMSS EDR Algorithm: Characterization, Optimization, and Validation

The Cross-track Infrared Sounder (CrIS) and the Advanced Technology Microwave Sounder (ATMS) instruments aboard the Suomi National Polar-orbiting Partnership satellite provide high-quality hyperspectral infrared and microwave observations to retrieve atmospheric vertical temperature and moisture profiles (AVTP and AVMP) and many other environmental data records (EDRs). The official CrIS and ATMS EDR algorithm, together called the Cross-track Infrared and Microwave Sounding Suite (CrIMSS), produces EDR products on an operational basis through the interface data processing segment. The CrIMSS algorithm group is to assess and ensure that operational EDRs meet beta and provisional maturity requirements and are ready for stages 1–3 validations. This paper presents a summary of algorithm optimization efforts, as well as characterization and validation of the AVTP and AVMP products using the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis, the Atmospheric Infrared Sounder (AIRS) retrievals, and conventional and dedicated radiosonde observations. The global root-mean-square (RMS) differences between the CrIMSS products and the ECMWF show that the AVTP is meeting the requirements for layers 30–300 hPa (1.53 K versus 1.5 K) and 300–700 hPa (1.28 K versus 1.5 K). Slightly higher RMS difference for the 700 hPa-surface layer (1.78 K versus 1.6 K) is attributable to land and polar profiles. The AVMP product is within the requirements for 300–600 hPa (26.8% versus 35%) and is close in meeting the requirements for 600 hPa-surface (25.3% versus 20%). After just one year of maturity, the CrIMSS EDR products are quite comparable to the AIRS heritage algorithm products and show readiness for stages 1–3 validations.

Seven Years' Observation of Mid-Upper Tropospheric Methane from Atmospheric Infrared Sounder

NASA/Jet Propulsion Laboratory, Pasadena, CA, USA; E-Mail: Thomas.s.pagano@jpl.nasa.gov * Author to whom correspondence should be addressed; E-Mail: Xiaozhen.xiong@noaa.gov; Tel.: +1-301-316-5020; Fax: +1-301-238-2398. Received: 20 September 2010; in revised form: 28 October 2010 / Accepted: 5 November 2010 / Published: 9 November 2010 Abstract: The Atmospheric Infrared Sounder (AIRS) on EOS/Aqua platform provides a measurement of global methane (CH

An Experiment Using High Spectral Resolution CrIS Measurements for Atmospheric Trace Gases: Carbon Monoxide Retrieval Impact Study

We perform a demonstration experiment using the National Oceanic Atmospheric Administration Unique Cross-track Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder Processing System to assess the improvement on trace gas retrievals upon switching to high spectral resolution CrIS radiance measurements (0.625 cm-1). The focus of this study is carbon monoxide retrievals. The experimental high spectral resolution CO retrievals show a remarkable improvement, of almost up to one order of magnitude in the degree of freedom of the signal, with respect to the low-resolution mode. Furthermore, high-resolution CO retrievals show similar skill with respect to existing CO operational products from the Atmospheric InfraRed Sounder, Atmospheric Sounder Interferometer, and Measurements of Pollution In The Troposphere instruments, both in terms of spatial variability and degrees of freedom. The results of this research provide evidence to support the need for high spectral resolution CrIS measurements. This is a fundamental prerequisite in guaranteeing continuity to the CO afternoon orbit monitoring as part of a multisatellite uniformly integrated long-term data record of atmospheric trace gases.

Ozone Profile Retrieval from an Advanced Infrared Sounder: Experiments with Tropopause-Based Climatology and Optimal Estimation Approach

Abstract Motivated by a significant potential for retrieving atmospheric ozone profile information from advanced satellite infrared sounders, this study investigates various methods to optimize ozone retrievals. A set of retrieval experiments has been performed to assess the impact of different background states (or the a priori states) and retrieval algorithms on the retrieved ozone profiles in the upper troposphere and lower stratosphere (UTLS) using Atmospheric Infrared Sounder (AIRS) measurements. A new tropopause-based ozone climatology, using publicly available global ozonesonde data to construct the a priori state, is described. Comparisons are made with the AIRS version 5 (v5) ozone climatology. The authors also present the result of a newly implemented optimal estimation (OE) algorithm and compare it to the current AIRS science team (AST) algorithm used in version 5. The ozone climatology using tropopause-referenced coordinates better preserves the shape and the magnitude of the ozone gradient ac...

A Critical Examination of Satellite Cloud Retrieval from AVHRR in the Arctic Using SHEBA Data

Abstract This study examines the validity and limitations associated with retrieval of cloud optical depth τ and effective droplet size re in the Arctic from Advanced Very High Resolution Radiometer (AVHRR) channels 2 (0.725–1.10 μm), 3 (3.55–3.93 μm), and 4 (10.3–11.3 μm). The error in re is found to be normally less than 10%, but the uncertainty in τ can be more than 50% for a 10% uncertainty in the satellite-measured radiance. Model simulations show that the satellite-retrieved cloud optical depth τsat is overestimated by up to 20% if the vertical cloud inhomogeneity is ignored and is underestimated by more than 50% if overlap of cirrus and liquid water clouds is ignored. Under partially cloudy conditions, τsat is larger than that derived from surface-measured downward solar irradiance (τsurf) by 40%–130%, depending on cloud-cover fraction. Here, τsat derived from NOAA-14 AVHRR data agrees well with τsurf derived from surface measurements of solar irradiance at the Surface Heat Budget of the Arctic Oce...

Retrieval of nitrous oxide from Atmospheric Infrared Sounder: Characterization and validation

This paper presents the retrieval algorithm of nitrous oxide (N2O) using the Atmospheric Infrared Sounder (AIRS) on EOS/Aqua, its validation using aircraft measurements, and one possible application for monitoring the global N2O annual trend from 2003 to 2013. The results demonstrate that AIRS is sensitive to N2O in the middle to upper troposphere, with the peak vertical sensitivity between 200 and 750 hPa and the sensitivity in the tropics larger than in the high-latitude regions. The degrees of freedom of the N2O retrieval are mostly between 1.0 and 1.5. Validation using the aircraft measurement profiles by the High-Performance Instrumented Airborne Platform for Environmental Research Pole-to-Pole Observations program over the Pacific Ocean indicated that the retrieval RMS error is mostly less than 8 ppb (or ~2.1%). One important feature is that the variability of N2O from AIRS is more than 2 times than that of the aircraft measurements in the lower troposphere. In agreement with surface measurements, a nearly linear trend of N2O can be obtained based on limited AIRS data of 1 day in 15 May in each year from 2003 to 2013, and the increase rate of N2O is about 0.72 ppb yr−1. This algorithm will be implemented in AIRS operational retrieval system, enabling the derivation of the N2O for over 20 years using the AIRS, the Infrared Atmospheric Sounding Interferometer, and the Cross-track Infrared Sounder. Such a unique product will be complementary to currently sparse ground-based observations for monitoring the N2O trend associated with climate change.

Retrieving atmospheric temperature and moisture profiles from SUOMI NPP CrIS/ATMS sensors using CrIMSS EDR algorithm

As a part of the Joint Polar Satellite System (JPSS) and the Suomi National Polar-orbiting Partnership (NPP), the Cross-track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) instruments make up the Cross-track Infrared and Microwave Sounder Suite (CrIMSS). CrIMSS primarily provides globally-referenced calibrated radiances and vertical profiles of temperature, moisture, and pressure. The CrIMSS operational code has been ported to various LINUX systems and retrievals are performed using both proxy and real ATMS/CrIS data. The high quality proxy data generated from the IASI instrument provided useful testing for the CrIMSS EDR algorithm prior to the launch of the SUOMI NPP satellite. The experience learned from processing the proxy data helped us to handle the SUOMI NPP CrIS/ATMS data as soon as they became available to the CAL/VAL team. In this paper, encouraging preliminary results of applying the ported CrIMSS EDR algorithm to the SUOMI NPP CrIS/ATMS data are presented.

Validation of Atmospheric Infrared Sounder (AIRS) temperature, water vapor, and ozone retrievals with matched radiosonde and ozonesonde measurements and forecasts

An evaluation of the temperature, water vapor, and ozone profile retrievals from the AIRS data is performed with more than three years of collocated radiosondes (RAOBs) and ozonesonde (O3SND) measurements. The Aqua-AIRS version 4.0 retrievals, global RAOB and O3SND measurements, forecast data from the NCEP_GFS, ECMWF, and the NOAA- 16 ATOVS retrievals are used in this validation and relative performance assessment. The results of the inter-comparison of AIRS temperature, water vapor and ozone retrievals reveal very good agreement with the measurements from RAOBs and O3SND s. The temperature RMS difference is close to the expected product goal accuracies, viz. 1oK in 1 km layers for the temperature and close to 15% in 2-km layers for the water vapor in the troposphere. The AIRS temperature retrieval bias is a little larger than the biases shown by the ATOVS, NCEP_GFS, and ECMWF forecasts. With respect to the ozone profile retrieval, the retrieval bias and RMS difference with O3SNDs is less than 5% and 20% respectively for the stratosphere. The total ozone from the AIRS retrievals matches very well with the Dobson/Brewer station measurements with a bias less than 2%. Overall, the analysis performed in this paper show a remarkable degree of confidence in the AIRS retrievals.