# Airborne Sunphotometry in the SAFARI 2000 Dry Season Campaign

**Report for the SAFARI 2000 Workshop held May 30-31, 2001**

**at Goddard Space Flight Center, Greenbelt, MD**

Philip B. Russell^1^, Beat Schmid^2^ and Jens Redemann^2^

^1^NASA Ames Research Center, Moffett Field, CA

^2^Bay Area Environmental Research Institute, San Francisco, CA

May 22, 2001

As requested by the meeting guidelines, this report gives a 2-page
summary with representative figures outlining progress in analyzing our
measurements from the 2000 campaign(s), a schedule for completing our
analyses, suggestions/desires for collaboration with other researchers
on scientific papers to report results, and a list of submitted
abstracts or titles of research through the next 6-8 months.

**Measurements and analyses, 2000 Dry Season Campaign.** We participated
in the 2000 Dry Season Campaign from August 13 to September 25 by making
measurements with the 14-channel NASA Ames Airborne Tracking
Sunphotometer (AATS-14) aboard the University of Washington CV-580
during 24 data flights based at Pietersburg, South Africa; Kasane,
Botswana; and Walvis Bay, Namibia. AATS-14 measures the transmission of
the direct solar beam at 14 discrete wavelengths (350-1558 nm) from
which we derive spectral aerosol optical depths (AOD) and columnar water
vapor (CWV). Flying at different altitudes over a fixed location allows
derivation of layer AOD and CWV. Data taken during feasible vertical
profiles allows derivation of aerosol extinction and water vapor
density. Measurements are summarized in the table at
<http://geo.arc.nasa.gov/sgg/SAFARI/> (see also excerpt on p.2).

Examples of AATS-14 data are shown in Figures 1 and 2. Figure 1 shows an
AOD profile at 12 wavelengths flown on September 6, 2000 near Mongu,
Zambia. The AOD values measured during this profile rank among the
highest encountered by the CV-580 during SAFARI-2000. Note that at the
top altitude of 4.8 km (geometric altitude) the AOD at 500 nm is still
0.17. Also shown in Figure 1 is the corresponding aerosol extinction
profile derived by differentiating smoothed spline fits to the optical
depth profiles. Although the extinctions are high throughout, the
profile seems to suggest a three-layer structure. At all altitudes, the
AOD is strongly dependent on wavelength: an indication of the presence
of smaller particles, presumably smoke.

Figure 2 shows the corresponding CWV and derived water vapor density
profile. Above 3 km the water vapor density and the AODs are correlated.
At the present stage of the analyses, we are unable to tell if this is
caused by advection of airmasses or by hygroscopic growth of the
aerosols.

**Schedule for completing analyses**

• AATS-14 data reduction to AOD(λ), Column H~2~O: First release for all
flights: Sep 2001; Final version: Sep 2002.

• Journal publications submitted, including collaborative analyses:
according to SAFARI publication schedule

**Suggestions/desires for collaboration with other researchers on papers
to report results**

[P. Pilewskie]{.underline} et al. (SSFR solar spectral forcing as a
function of aerosol thickness); [P. Hobbs]{.underline} et al. (CV-580 in
situ comparisons); [B. Holben]{.underline} et al. (AERONET comparisons);
[J. Welton]{.underline} et al. (MPL comparisons and derivation of
complex refractive index); M. McGill, J. Spinhirne et al. (ER-2 lidar
comparisons and joint analyses); L. Remer et al. (MODIS comparisons); J.
Herman, O. Torres et al. (TOMS comparisons); C. Bruegge, R. Kahn (MISR,
AirMISR comparisons); S. Platnick (MAS, dust outbreak over coastal
stratus); R. Bruintjes (Aerocommander, CV-580 in situ comparisons).
[\[Underlining indicates collaboration already in
progress.\]]{.underline}

## List of submitted abstracts or titles of research through the next 6-8 months.

Schmid, B., P. B. Russell, P. Pilewskie, J. Redemann, J. M. Livingston,
P. V. Hobbs, E. J. Welton, J. Campbell, B. N. Holben, M. McGill, J.
Spinhirne, Airborne sunphotometry and closure studies in SAFARI-2000 dry
season campaign, Accepted for presentation, 8^th^ Scientific Assembly of
IAMAS, Innsbruck, Austria, 10-18 July, 2001.

Schmid, B. et al., \[title and coauthors similar to above\], Abstract to
be submitted (by 15 June 2001 deadline) to Safari 2000 Science
Symposium, Siavonga, Zambia, 28-31 August, 2001.

Related papers will be submitted to:

• 4^th^ Global Aerosol Climatology Program (GACP) Science Team Meeting,
Ann Arbor, MI, 24-26 Oct 2001

• EOS Inter-Disciplinary Science (EOS-IDS) Team Meeting, early November
2001

• Fall AGU Meeting, San Francisco, CA, 10-14 December 2001

![](media/image1.pct){width="9.210416666666667in" height="1.725in"}

![](media/image2.pct){width="4.629861111111111in"
height="3.0861111111111112in"}

**Figure 1:** Left panel: Aerosol optical depth profiles calculated from
AATS-14 measurements (13 wavelengths shown) acquired during an aircraft
ascent near Mongu, Zambia. Right panel: Corresponding aerosol extinction
profiles derived by differentiating spline fits (dashed lines in left
panel) to the optical depth profiles

![](media/image3.pct){width="4.580555555555556in"
height="2.998611111111111in"}

**Figure 2:** Columnar water vapor and water vapor density profile
retrieved during same ascent as shown in Figure 1.