James N. Howell

High-Resolution Doppler Lidar for Boundary Layer and Cloud Research

Abstract The high-resolution Doppler lidar (HRDL) was developed to provide higher spatial, temporal, and velocity resolution and more reliable performance than was previously obtainable with CO2-laser-based technology. The improved performance is needed to support continued advancement of boundary layer simulation models and to facilitate high-resolution turbulent flux measurements. HRDL combines a unique, eye-safe, near-IR-wavelength, solid-state laser transmitter with advanced signal processing and a high-speed scanner to achieve 30-m range resolution and a velocity precision of ∼10 cm s−1 under a variety of marine and continental boundary layer conditions, depending on atmospheric and operating conditions. An attitude-compensating scanner has been developed to facilitate shipboard marine boundary layer observations. Vertical velocities, fine details of the wind profile near the surface, turbulence kinetic energy profiles, and momentum flux are measurable with HRDL. The system is also useful for cloud s...

The Multi-center Airborne Coherent Atmospheric Wind Sensor

Abstract In 1992 the atmospheric lidar remote sensing groups of the National Aeronautics and Space Administration Marshall Space Flight Center, the National Oceanic and Atmospheric Administration/Environmental Technology Laboratory (NOAA/ETL), and the Jet Propulsion Laboratory began a joint collaboration to develop an airborne high-energy Doppler laser radar (lidar) system for atmospheric research and satellite validation and simulation studies. The result is the Multi-center Airborne Coherent Atmospheric Wind Sensor (MACAWS), which has the capability to remotely sense the distribution of wind and absolute aerosol backscatter in three-dimensional volumes in the troposphere and lower stratosphere. A factor critical to the programmatic feasibility and technical success of this collaboration has been the utilization of existing components and expertise that were developed for previous atmospheric research by the respective institutions. For example, the laser transmitter is that of the mobile ground-based Do...

Remote sensing of multi-level wind fields with high-energy airborne scanning coherent Doppler lidar

The atmospheric lidar remote sensing groups of NOAA Environmental Technology Laboratory, NASA Marshall Space Flight Center, and Jet Propulsion Laboratory have developed and flown a scanning, 1 Joule per pulse, CO2 coherent Doppler lidar capable of mapping a three-dimensional volume of atmospheric winds and aerosol backscatter in the planetary boundary layer, free troposphere, and lower stratosphere. Applications include the study of severe and non-severe atmospheric flows, intercomparisons with other sensors, and the simulation of prospective satellite Doppler lidar wind profilers. Examples of wind measurements are given for the marine boundary layer and near the coastline of the western United States.

Airborne Doppler lidar investigation of the wind-modulated sea-surface angular retroreflectance signature

Concurrent measurements of sea-surface retroreflectance and associated wind velocity acquired with an airborne CO2 Doppler lidar are described. These observations provide further insight into thermal infrared optical phenomenology of air-sea interface processes, contribute to a greater understanding of radiation transfer between the atmosphere and the hydrosphere, and enable improved models of wind-driven ocean-surface stress applicable to other remote sensing applications. In particular, we present lidar measurements of azimuthally anisotropic reflectance behavior and discuss the implications to current understanding of sea-surface optical properties.

Radiometric calibration of an airborne CO2 pulsed Doppler lidar with a natural earth surface.

Radiometric calibration of an airborne CO2 pulsed Doppler lidar has been accomplished with surface retroreflection signals from the White Sands National Monument, New Mexico. Two circular passes were made at altitudes of 6.3 and 9.3 km. The computed calibration factors for both altitudes are in excellent agreement with the value derived from standard ground-based measurements involving a fixed sandpaper target of known reflectance. This finding corroborates a previous study that successfully calibrated an airborne cw Doppler lidar with a variety of natural Earth surfaces. The present results indicate that relatively uniform Earth surface targets can be used for in-flight calibration of CO2 pulsed airborne and, in principal, other infrared lidars.

Transportable Lidar for the measurement of ozone concentration and aerosol profiles in the lower troposphere

A very compact, transportable differential absorption lidar (DIAL) for ozone and aerosol profiling in the lower troposphere (from near surface to about 3 km) has been developed at the National Oceanic and Atmospheric Administrations Environmental Technology Laboratory. The ozone lidar has been employed in two field experiments in California. the first was in intercomparison experiment of the lidar and an airborne ozone analyzer carried out in the Sacramento valley of northern California during July 1993. The second field experiment involving the ozone lidar was the Free Radical Study, carried out in the Los Angeles basin during September 1993, where the highest ozone episode of the year was observed during the experiment. The system will be described and examples of ozone profiles during the high- ozone episode in inland Los Angeles will be shown.

Multicenter airborne coherent atmospheric wind sensor (MACAWS) instrument: recent upgrades and results

The Multicenter Airborne Coherent Atmospheric Wind Sensor instrument is an airborne coherent Doppler laser radar (Lidar) capable of measuring atmospheric wind fields and aerosol structure. Since the first demonstration flights onboard the NASA DC-8 research aircraft in September 1995, two additional science flights have been completed. Several system upgrades have also bee implemented. In this paper we discuss the system upgrades and present several case studies which demonstrate the various capabilities of the system.

Overview of the first Multicenter Airborne Coherent Atmospheric Wind Sensor (MACAWS) experiment: conversion of a ground-based lidar for airborne applications

The first Multi center Airborne Coherent Atmospheric Wind Sensor (MACAWS) field experiment demonstrated an airborne high energy TEA CO2 Doppler lidar system for measurement of atmospheric wind fields and aerosol structure. The system was deployed on the NASA DC-8 during September 1995 in a series of checkout flights to observe several important atmospheric phenomena, including upper level winds in a Pacific hurricane, marine boundary layer winds, cirrus cloud properties, and land-sea breeze structure. The instrument, with its capability to measure 3D winds and backscatter fields, promises to be a valuable tool for climate and global change, severe weather, and air quality research. In this paper, we describe the airborne instrument, assess its performance, discuss future improvements, and show some preliminary results from the September experiments.